Semiconductor laser device, and method of manufacturing the same

ABSTRACT

A semiconductor laser device comprises a laminate consisting of a semiconductor layer of first conductivity type, an active layer and a semiconductor layer of second conductivity type, which is different from the first conductivity type, that are stacked in order, with a waveguide region being formed to guide a light beam in a direction perpendicular to the direction of width by restricting the light from spreading in the direction of width in the active layer and in the proximity thereof, wherein the waveguide region has a first waveguide region and a second waveguide region, the first waveguide region is a region where light is confined within the limited active layer by means of a difference in the refractive index between the active layer and the regions on both sides of the active layer by limiting the width of the active layer, and the second waveguide region is a region where the light is confined therein by providing effective difference in refractive index in the active layer.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a semiconductor laser devicehaving stripe ridge being formed. More particularly, the presentinvention relates to a semiconductor laser device which uses GaN, AlN orInN, or the Group III-V nitride compound semiconductor(In_(b)Al_(d)Ga_(1−b−d)N, 0≦b, 0≦d, b+d<1) that is a mixed crystal ofthe compounds described above.

DESCRIPTION OF RELATED ARTS

[0002] Recently, nitride semiconductor laser devices have been receivingincreasingly demands for the applications in optical disk systems suchas DVD which are capable of recording and reproducing a large amount ofinformation with a high density. Accordingly, vigorous research effortsare being made in the field of nitride semiconductor laser device.Because of the capability to oscillate and emit visible light over abroad spectrum ranging from ultraviolet to red, the nitridesemiconductor laser device is expected to have wide applications such aslight sources for laser printer and optical network, as well as theoptical disk system.

[0003] With regard to the structure of the laser device, in particular,various researches have been made and a number of proposals have beenmade for the structure that enables preferable control of transverseoscillation mode. Among these, ridge waveguide structure is viewed aspromising, and is employed in the nitride semiconductor laser devicethat was shipped first in the world.

[0004] The ridge waveguide structure for a semiconductor laser devicemakes it easier to drive laser oscillation due to the simple structure,although variations are likely to occur in the characteristics of thedevices during volume production. This is because the characteristicsare caused to vary by variations in the dimensions of mesa stripe in thecase of ridge waveguide structure, while the dimensional accuracy of themesa stripe is determined by the accuracy of etching and the dimensionalaccuracy of the mesa stripe cannot be made higher than the accuracy ofetching. In the case of a semiconductor laser device made from asemiconductor material which is likely to suffer significant etchingdamage in the active layer or damage caused by exposing the active layersurface to the etching atmosphere, laser characteristics degrade due tothe etching damage in the active layer and on the active layer surfacewhen a semiconductor laser device of perfect refractive index guidedtype is made by etching deeper than the active layer thereby formingridges. Therefore, such a semiconductor laser device must be made in theeffective refractive index type waveguide structure wherein stripes areformed to a depth that does not reach the active layer. However, in thecase of effective refractive index type waveguide structure, variationsin the device characteristics due to the variation in the stripeconfiguration mentioned above become significant, thus resulting inconsiderable variations in the device characteristics during volumeproduction.

[0005] In order to apply the nitride semiconductor laser device in thefields described previously, it is indispensable to provide a devicewhich can be mass-produced with stable quality.

[0006] However, the structure of the laser devices known at present hasa bottle neck in the formation of the ridge waveguide. This is because,while the ridge waveguide is formed by growing nitride semiconductorthat constitutes the device, then removing a part of the nitridesemiconductor by etching the upper layer thereby forming the ridge whichconstitutes the waveguide, accuracy of the etching has a great effect onthe characteristics of the laser device obtained as mentionedpreviously. That is, since the transverse mode is controlled by theconfiguration, particularly height and width, of the ridge thatconstitutes the ridge waveguide and the far field pattern (F.F.P.) ofthe laser beam is determined accordingly, an error in the control of thedepth of etching when forming the ridge waveguide is a major factorwhich directly causes variations in the device characteristics.

[0007] Dry etching techniques such as reactive ion etching (RIE) havebeen known for etching nitride semiconductor, but it has been difficultto control the depth of etching to such an accuracy as to completelysolve the problem of variations in the device characteristics with theseetching techniques.

[0008] Design of devices in recent years in a trend to have a multitudeof layers that are controlled to be several atoms in thickness formed inthe device, such as in the case of super lattice structure. This alsocontributes to the variations in the device characteristics caused bythe etching accuracy. Specifically, when forming the layers whichconstitute the device structure, the layers are formed with an extremelyhigh accuracy and it is difficult to achieve the device structure ofsophisticated design by forming the ridge and other structure with theetching technique having an accuracy lower than the accuracy of filmforming by several orders of magnitude, thus making an obstacle to theimprovement of device characteristics.

[0009] For example, when forming a nitride semiconductor laser devicehaving a high output power in the refractive-index guiding typestructure where ridge waveguide is provided on the active layer withoutetching the active layer, accuracy of etching depth must be controlledso as to keep the effective difference in refractive index between aportion of the active layer right below the ridge and other portion ofthe active layer to one hundredth. In order to achieve this accuracy,the ridge must be formed by etching while controlling the depth with anaccuracy within 0.01 μm till a very small portion of p-type claddinglayer remains, in case the layer right above the active layer is thep-type cladding layer. On the other hand, width of the ridge waveguidemay have lower accuracy but must be etched with an accuracy of 0.1 μm.

[0010] When the RIE process is employed for etching the nitridesemiconductor, the layer exposed by etching and the surface thereof areprone to damage, which leads to deterioration of the devicecharacteristics and reliability. Etching can be done in a wet etchingprocess as well as a dry etching process, although wet etching solutionwhich is applicable to nitride semiconductors has not been developed.

[0011] As described above, whether nitride semiconductor laser devicehaving high functionality can be made or not in volume production withless variations in the characteristics heavily depends on the accuracyof forming the ridge waveguide in the etching process, and it hascritical importance to form the ridge waveguide with a high accuracy.

[0012] In light of the circumstances described above, the presentinventors have invented a laser device or an end face light emissiondevice and a method for manufacturing the same which, even in the caseof a semiconductor laser device of stripe configuration and despite thesemiconductor laser device has a resonator of excellent oscillation andwave guiding characteristics, allows stable control of transverse modeand is capable of emitting laser beam of excellent F.F.P., with lessvariations in the device characteristics even when mass-produced.

SUMMARY OF THE INVENTION

[0013] An object of the present invention can be achieved with thesemiconductor laser device of the present invention having such aconstitution as described below.

[0014] A first semiconductor laser device of the present inventioncomprises a laminate consisting of a semiconductor layer of firstconductivity type, an active layer and a semiconductor layer of secondconductivity type, which is different from the first conductivity type,that are stacked in order, with a waveguide region being formed to guidea light beam in a direction perpendicular to the direction of width byrestricting the light from spreading in the direction of width in theactive layer and in the proximity thereof, wherein the waveguide regionhas a first waveguide region and a second waveguide region, the firstwaveguide region is a region where light is confined within the limitedactive layer by means of a difference in the refractive index betweenthe active layer and the regions on both sides of the active layer bylimiting the width of the active layer, and the second waveguide regionis a region where the light is confined therein by providing effectivedifference in refractive index in the active layer.

[0015] In the first semiconductor laser device of the present inventionconstituted as described above, since the waveguide region has the firstwaveguide region where light is confined within the active layer byactually providing a difference in the refractive index between theactive layer and the regions on both sides of the active layer,oscillation in the transverse mode can be more surely suppressed in thefirst waveguide region and the beam can be controlled reliably therebyemitting laser beam having excellent F.F.P.

[0016] Also in the first semiconductor laser device which has the secondwaveguide region constituted by forming a region that has effectivelyhigh refractive index in the active layer, since the waveguide can beformed without exposing the active layer that functions as the waveguidedirectly to the outside in the second waveguide, service life of thedevice can be prolonged and reliability can be improved. Thus the firstsemiconductor laser device of the present invention has the features ofthe first waveguide region and the second waveguide region combined.

[0017] In the first semiconductor laser device of the present invention,the active layer in the first waveguide region can be constituted byforming a first ridge that includes the active layer thereby limitingthe width of the active layer, and the region having effectively higherrefractive index can be constituted by forming a second ridge in thelayer of the second conductivity type.

[0018] Also in the first semiconductor laser device of the presentinvention, the first ridge can be formed by etching both sides of thefirst ridge till the layer of the first conductivity type is exposed andthe second ridge can be formed by etching both sides of the second ridgeso that the layer of the second conductivity type remains on the activelayer.

[0019] In the first semiconductor laser device of the present invention,thickness of the layer of the second conductivity type located on theactive layer on both sides of the second ridge is preferably 0.1 μm orless, in which case it is made possible to more surely control thetransverse mode.

[0020] Further in the first semiconductor laser device of the presentinvention, the second ridge is preferably longer than the first ridge,in which case the reliability can be improved further.

[0021] Further in the first semiconductor laser device of the presentinvention, the first waveguide region preferably includes one resonanceend face of the laser resonator in which case laser beam of excellentF.F.P. can be obtained.

[0022] Also in the first semiconductor laser device of the presentinvention, it is preferable to use the one resonance end face as thelight emitting plane, in which case laser beam of more excellent F.F.P.can be obtained.

[0023] In the first semiconductor laser device of the present invention,length of the first waveguide region is preferably 1 μm or more.

[0024] Further in the first semiconductor laser device of the presentinvention, the semiconductor layer of the first conductivity type, theactive layer and the semiconductor layer of the second conductivity typecan be formed from nitride semiconductor.

[0025] Also in the semiconductor laser device described above, theactive layer can be constituted from a nitride semiconductor layer whichincludes In, in which case the laser can be oscillated in the visibleregion of relatively short wavelength and in the ultraviolet region.

[0026] In the first semiconductor laser device of the present invention,it is preferable to form insulation films on both sides of the firstridge and on both sides of the second ridge, while the insulation filmis made of a material selected from the group consisting of oxides ofTi, V, Zr, Nb, Hf and Ta and compounds SiN, BN, SiC and AlN.

[0027] A second semiconductor laser device of the present inventioncomprises a laminate which consists of a layer of the first conductivitytype, an active layer and a layer of the second conductivity type thatis different from the first conductivity type being stacked in order,and is provided with a stripe waveguide region, wherein the stripewaveguide region has at least a first waveguide region C₁ in which astripe-shaped waveguide based on absolute refractive index is providedand a second waveguide region C₂ in which a stripe-shaped waveguidebased on effective refractive index is provided, which are arranged inthe direction of the resonator. In this constitution, since the laserdevice of the present invention has the second waveguide region C₂having excellent device reliability and the first waveguide region C₁having excellent controllability of the transverse oscillation andexcellent beam characteristic, the laser device combines both of thesecharacteristics thus making it possible to provide various laser devicesaccording to the application without tedious modification of the devicedesign. In the effective refractive index type waveguide, a stripe ridgeformed in the layer of the second conductivity type located on theactive layer makes it possible to keep the active layer remain in thestate of growing, so that the waveguide does not deteriorate whenoperating the device, thus ensuring excellent reliability of the device.Also because the first waveguide region C₁ of refractive index guidingtype is provided in the waveguide by etching deeper than the activelayer thereby creating a difference in the refractive index on bothsides of the waveguide region, the transverse mode can be easilycontrolled. Providing this as the waveguide of the laser device makes itpossible to easily change the transverse mode in the waveguide. In thisspecification, the waveguide which has the first waveguide region willbe referred to as total refractive index type waveguide or absoluterefractive index type waveguide in order to avoid confusion with theeffective refractive index type waveguide.

[0028] In the second semiconductor laser device of the presentinvention, the absolute refractive index of the first waveguide regionC₁ is achieved by means of the stripe ridge which is provided so as toinclude the layer of the first conductivity type, the active layer andthe layer of the second conductivity type, and the effective refractiveindex of the second waveguide region C₂ is achieved by means of thestripe ridge which is provided in the layer of second conductivity type.With this constitution, since the first waveguide region C₁ and thesecond waveguide region C₂ can be formed easily in the laser device,laser devices of diverse characteristics can be made by simple design.

[0029] A third semiconductor laser device of the present inventioncomprises a laminate which consists of a layer of the first conductivitytype, an active layer and a layer of the second conductivity type thatis different from the first conductivity type being stacked in order,and is provided with a waveguide region of stripe configuration, whereinthe stripe waveguide region has at least a second waveguide region wherea portion of the layer of the second conductivity type is removed and astripe ridge is provided in the layer of the second conductivity type,and a first waveguide region C₁ where portions of the layer of secondconductivity type, the active layer and the layer of first conductivitytype are removed and a stripe ridge is provided in the layer of thefirst conductivity type, which are arranged in the direction ofresonator. With this constitution, since the stripe waveguide region isconstituted from the region (first waveguide region C₁) where a part ofthe active layer is removed and the region (second waveguide region C₂)where the active layer is not removed, damage to the active layer casedby the removal can be restrained within a part of the waveguide, therebyimproving the reliability of the device. For a semiconductor materialwhich is heavily subject to damage, deterioration in the reliability andcharacteristic of the device caused by the partial removal of the activelayer, a laser device having desired reliability and characteristic ofthe device can be achieved by designing the proportion occupied by thefirst waveguide region C₁, since the first waveguide region C₁ isprovided only partially. Also by changing the length of (proportion ofthe waveguide constituted from) and location of the first waveguideregion C₁ and the second waveguide region C₂, laser devices of variouscharacteristics can be made and, particularly, laser devices havingdesired beam characteristics can be easily obtained.

[0030] In the second and third semiconductor laser devices, the firstwaveguide region C₁ and the second waveguide region C₂ may also beconstituted by removing a part of the laminate structure and forming aridge waveguide comprising a stripe ridge. With this constitution, laserdevices of ridge waveguide structure comprising the stripe ridge havingdiverse characteristics can be made.

[0031] In the second and third semiconductor laser devices, it ispreferable to make the stripe of the second waveguide region C₂ longerthan the first waveguide region C₁. With this constitution, a laserdevice having excellent reliability can be made from a semiconductormaterial which undergoes greater deterioration due to the formation ofthe first waveguide region C₁, for example a semiconductor materialwhich is damaged when a part of the active layer is removed or exposedto the atmosphere.

[0032] Also in the second and third semiconductor laser devices, it ispreferable that at least one of the resonance end faces of thesemiconductor laser device is formed at the end of the first waveguideregion C₁. With this constitution, by providing the first waveguideregion C₁ having excellent controllability of the transverse mode on oneof the resonance end faces, guiding of light can be controlled moreeffectively than in the case of providing the first waveguide region C₁at other position, thereby making it possible to obtain laser deviceshaving diverse characteristics.

[0033] Also in the second and third semiconductor laser devices, it ispreferable that the resonance end face formed on the end of the firstwaveguide region C₁ is the light emitting plane. With this constitution,by providing the first waveguide region C₁ which has excellentcontrollability of transverse mode on the laser beam emitting plane,beam characteristic can be directly controlled and a laser device havingdesired F.F.P. and laser beam aspect ratio can be obtained.

[0034] Also in the second and third semiconductor laser devices, it ispreferable that length of the stripe of the first waveguide region C₁which has the resonance end face on the end face thereof is preferably 1μm or longer. With this constitution, more reliable control of F.F.P.and laser beam aspect ratio can be achieved and the laser devices ofless variations in the characteristics are obtained.

[0035] The second and third semiconductor laser devices may also beconstituted by using a nitride semiconductor in the layer of the firstconductivity type, the active layer and the layer of the secondconductivity type. This constitution makes it possible to make laserdevices having diverse characteristics from the nitride semiconductor inwhich it is difficult to form a buried structure of regrowth layer byion implantation. Since the service life of the device becomessignificantly shorter when a part of the active layer is removed byetching or the like in nitride semiconductor, it has been difficult tocommercialize a laser device comprising total refractive index typewaveguide in which a part of the active layer is removed. However, sincea part of the waveguide becomes the first waveguide region C₁, a laserdevice having excellent controllability of the transverse mode can bemade while keeping the device life from decreasing.

[0036] In the second and third semiconductor laser devices, the activelayer may also be constituted from a nitride semiconductor laser whichincludes In. With this constitution, a laser device which oscillatesover a range of wavelengths from ultraviolet to visible light can bemade.

[0037] Also in the second and third semiconductor laser devices, thefirst waveguide region C₁ may include n-type nitride semiconductor andthe second waveguide region C₂ may include p-type nitride semiconductor.

[0038] Also in the second and third semiconductor laser devices, it ispreferable that the second waveguide region C₂ has a p-type claddinglayer which includes p-type nitride semiconductor and the stripe ridgeof the second waveguide region is formed while keeping the thickness ofthe p-type cladding layer is less than 0.1 μm. With this constitution, alaser device having low threshold current and excellent controllabilityof the transverse mode can be made. Here thickness of the p-typecladding layer refers to the distance between the exposed surface of thep-type cladding layer in a region where the ridge is not formed and theinterface with the adjacent layer below the p-type cladding layer, and“above the active layer” means the location above the interface betweenthe active layer and the adjacent layer located above. That is, in casethe active layer and the p-type cladding layer are provided in contactwith each other, the exposed surface mentioned above is formed at adepth in the p-type cladding layer where it remains with a thicknessgreater than 0 and within 0.1 μm. In case a guide layer or the like isprovided between the active layer and the p-type cladding layer as inthe case of the first embodiment to be described later, the exposedsurface mentioned above is formed above the interface between the activelayer and the adjacent layer located above, and below a depth in thep-type cladding layer where it remains with a thickness of 0.1 μm or ina layer between the active layer and the p-type cladding layer.

[0039] The second and third semiconductor laser devices may also havesuch a constitution as the nitride semiconductor is exposed on the sidefaces of the stripe ridge of the first waveguide region C₁ and on theside faces of the stripe ridge of the second waveguide region C₂, aninsulation film is provided on the side face of the stripe ridge, andthe insulation film is made of a material selected from the groupconsisting of oxides of at least one element selected from Ti, V, Zr,Nb, Hf and Ta and at least one kind of compounds SiN, BN, SiC and AlN.With this constitution, satisfactory difference of refractive index canbe provided in the stripe ridge of the nitride semiconductor laserdevice, and the laser device having the stripe waveguide region ofexcellent controllability of the transverse mode can be made.

[0040] In the second and third semiconductor laser devices, width of thestripe ridge is preferably in a range from 1 μm to 3 μm. With thisconstitution, the stripe waveguide region of excellent controllabilityof the transverse mode can be formed within the waveguide layer in thefirst waveguide region C₁ and the second waveguide region C₂, thusachieving a laser device free of kink in the current-optical outputcharacteristic.

[0041] A method for manufacturing the semiconductor laser device of thepresent invention achieves the object of the present invention in aconstitution described below.

[0042] The method for manufacturing the semiconductor laser device ofthe present invention comprises a laminating process in which the layerof the first conductivity type, the active layer and the layer of thesecond conductivity type are stacked in order by using nitridesemiconductor to form a laminate, a process of forming a firstprotective film of stripe configuration after forming the laminate, afirst etching process in which the laminate is etched in a portionthereof where the first protective film is not formed thereby to formthe stripe ridge in the layer of the second conductivity type, a secondetching process in which a third protective film is formed via the firstprotective film on a portion of the surface which has been exposed inthe first etching process and the laminate is etched in a portionthereof where the third protective film is not formed thereby to formthe stripe ridge in the layer of first conductivity type, a process inwhich a second protective film having insulating property made of amaterial different from the first protective film is formed on the sideface of the stripe ridge and on the nitride semiconductor surfaceexposed by etching, and a process of removing the first protective filmafter the second protective film has been formed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043]FIG. 1A is a perspective view schematically showing theconstitution of the laser device according to an embodiment of thepresent invention.

[0044]FIG. 1B is a sectional view of the second waveguide region of thelaser device of the embodiment.

[0045]FIG. 1C is a sectional view of the first waveguide region of thelaser device of the embodiment.

[0046]FIG. 2A is a schematic sectional view prior to forming the ridgein the laser device of the prior art.

[0047]FIG. 2B is a schematic sectional view after forming the ridge inthe laser device of the prior art.

[0048]FIG. 2C is partially enlarged view of a part denoted “a” in FIG.2B.

[0049]FIG. 2D is partially enlarged view of a part denoted “b” in FIG.2B.

[0050]FIG. 3A is a perspective view schematically showing theconstitution of layers in the laser device according to an embodiment ofthe present invention, and FIG. 3B is a side view of FIG. 3A.

[0051]FIG. 4A is a side view of the laser device of a variationaccording to the present invention.

[0052]FIG. 4B is a side view of the laser device of another variationaccording to the present invention.

[0053]FIG. 5A through FIG. 5D are perspective views showing the processof forming the ridge of the laser device of the present invention.

[0054]FIG. 5E is a sectional view of a portion where the secondwaveguide region of FIG. 5C is to be formed.

[0055]FIG. 5F is a perspective view of a portion where the secondwaveguide region of FIG. 5D is to be formed.

[0056]FIG. 6A through FIG. 6C are perspective views showing the processof forming the ridge of the laser device of the present invention by amethod different from the method shown in FIG. 5A through FIG. 5D.

[0057]FIG. 7A through FIG. 7D are perspective views showing the processof forming the electrodes in the laser device of the present invention.

[0058]FIG. 8 is a schematic sectional view of the second waveguideregion of the laser device according to the first embodiment of thepresent invention.

[0059]FIG. 9 is a schematic sectional view of the first waveguide regionof the laser device according to the first embodiment of the presentinvention.

[0060]FIG. 10 is a graph showing the acceptance ratio as a function ofthe depth of etching in the laser device of effective refractive indextype.

[0061]FIG. 11 is a graph showing the drive current as a function of thedepth of etching in the laser device of effective refractive index type.

[0062]FIG. 12 is a graph showing the service life as a function of thedepth of etching in the laser device of effective refractive index type.

[0063]FIG. 13A is a perspective view of the laser device according tothe sixth embodiment of the present invention.

[0064]FIG. 13B is a cross sectional view of the laser device accordingto the sixth embodiment of the present invention.

[0065]FIG. 14A is a perspective view of the laser device according tothe seventh embodiment of the present invention.

[0066]FIG. 14B is a sectional view of the second waveguide region of thelaser device according to the seventh embodiment of the presentinvention.

[0067]FIG. 14C is a sectional view of the first waveguide region of thelaser device according to the seventh embodiment of the presentinvention.

[0068]FIG. 15A is a perspective view of the laser device according tothe eighth embodiment of the present invention.

[0069]FIG. 15B is a cross sectional view of the laser device accordingto the eighth embodiment of the present invention.

[0070]FIG. 16A through FIG. 16D are perspective views showing the methodfor manufacturing the laser device of the present invention by usingdevices formed on a wafer.

[0071]FIG. 17A and FIG. 17B are schematic sectional views showing thecutting position according to the method for manufacturing the laserdevice of the present invention.

[0072]FIG. 18 is a schematic diagram showing the process of forming thereflector film according to the method for manufacturing the laserdevice of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0073] Now the semiconductor laser device of the present invention willbe described below by way of preferred embodiments with reference to theaccompanying drawings.

[0074] The semiconductor laser device of an embodiment according to thepresent invention has a first waveguide region C₁ and a second waveguideregion C₂ as stripe waveguide region as shown in FIG. 1A.

[0075] The first waveguide region C₁ is a waveguide region where a ridge(first ridge 201) is formed so as to include an active layer 3 and adifference in the refractive index is created between the active layer 3and the regions (in the atmosphere in this case) located on both sidesthereof as shown in FIG. 1C, thereby to confine light within the activelayer 3. In this specification, the waveguide region where light isconfined by providing an actual difference in the refractive indexbetween the active layer and the regions on both sides thereof will bereferred to as the total refractive index type waveguide.

[0076] The second waveguide region C₂ is a waveguide region where aridge (second ridge 202) is formed in the semiconductor layer located onthe active layer so that the effective refractive index of the activelayer 3 located below the second ridge 202 is made higher than that ofthe active layer located on both sides thereof as shown in FIG. 1B,thereby to confine light within the active layer 3 having highereffective refractive index. In this specification, the waveguide regionwhere light is confined by providing an effective difference in therefractive index between the active layer and the regions on both sidesthereof will be referred to as the effective refractive index typewaveguide.

[0077] The semiconductor laser according to the present invention ischaracterized by the total refractive index type waveguide and theeffective refractive index type waveguide provided in the waveguide.

[0078] Specifically, the second waveguide region C₂ is constituted byforming the laminate consisting of the layer of the first conductivitytype, the active layer and the layer of the second conductivity typewhich is different from the first conductivity type being stacked one onanother, and forming the second stripe ridge 202 on the layer 2 of thesecond conductivity type to such a depth as the active layer is notreached, and the first waveguide region C₁ is constituted by forming thefirst stripe ridge 201 so as to include portions of the layer 2 of thesecond conductivity type, the active layer 3 and the layer 1 of thefirst conductivity type.

[0079] According to the present invention, by having the first waveguideregion C₁ and the second waveguide region C₂ in the waveguide asdescribed above, semiconductor laser devices of diverse characteristicscan be obtained. In the semiconductor laser device of the presentinvention, the waveguide having the first waveguide region C₁ and thesecond waveguide region C₂ can be formed in various forms as shown inFIGS. 3 and 4. FIG. 3A is a partially cutaway perspective view of thelaser device of such a structure as the stripe ridge is formed byremoving a part of the laminate. FIG. 3B is a cross section viewed inthe direction of arrow in FIG. 3A. FIGS. 4A and 4B show a waveguidestructure different from that shown in FIG. 3.

[0080] According to the present invention, as shown in FIGS. 3 and 4,various constitutions can be employed where the first waveguide regionC₁ and the second waveguide region C₂ are disposed in variousarrangements in the resonator direction (longitudinal direction of thestripe ridge). The semiconductor laser according to the presentinvention may also have a waveguide region other than the firstwaveguide region C₁ and the second waveguide region C₂, as a matter offact. For example, a waveguide region 203 different from the firstwaveguide region C₁ and the second waveguide region C₂ may be providedbetween the first waveguide region C₁ and the second waveguide region C₂as shown in FIG. 4A. FIG. 3 shows such a structure as the firstwaveguide region C₁ is provided so as to include one of the resonanceend faces of the resonator and the second waveguide region C₂ isprovided so as to include the other resonance end face. FIG. 4A shows asemiconductor laser device having such a structure as the first ridge201 which constitutes the first waveguide region C₁ and the secondstripe ridge 202 which constitutes the second waveguide region C₂ arejoined via a waveguide region 203 which is formed so as to incline withrespect to the vertical direction (perpendicular to the resonatordirection). Thus the first waveguide region C₁ and the second waveguideregion C₂ may be formed either substantially continuously in theresonator direction as shown in FIG. 3 or with another region beinginterposed therebetween as shown in FIG. 4A.

[0081] According to the present invention, it is not necessary thatwidth of the first ridge 201 and width of the second ridge 202 aresubstantially the same. For example, in case the side face of each ridgeis formed to incline as shown in FIGS. 1 and 3, width at the base of thefirst ridge 201 provided to constitute the first waveguide region C₁ andwidth at the base of the second ridge 202 provided to constitute thesecond waveguide region C₂ become inevitably different from each other.The side face of the first ridge and the side face of the second ridgepreferably lie in the same plane. While the stripe ridges shown in FIG.1 and FIG. 3 are formed in the normal mesa configuration where the sidefaces are inclined so that width decreases from the base to the top, theridge may also be formed in the inverted mesa configuration where thewidth increases from the base to the top, and further both side faces ofthe mesa may be inclined either in the same way or in the oppositemanner.

[0082] Width of the top surface of the first ridge 201 and width of thetop surface of the second ridge 202 may be different from each other.Further, width of the first ridge 201 and width of the second ridge 202viewed in the horizontal section may be different so as to changediscontinuously at the border of the first ridge 201 and the secondridge 202.

[0083] [Resonator Structure]

[0084] In the semiconductor laser device of this embodiment, the stripewaveguide is constituted by removing a part of the laminate structureand forming the ridge. That is, as shown in FIGS. 1 and 3, the resonatorhas such a structure as the stripe ridge is formed by removing bothsides of a portion which would become the ridge by etching or othermeans in the laminate consisting of the layer 1 of the firstconductivity type, the active layer 3 and the layer 2 of the secondconductivity type, which is suited to the so-called ridge waveguidelaser device. According to the present invention, since at least thefirst waveguide region C₁ and the second waveguide region C₂ areprovided by means of the stripe ridge, beam characteristic can beimproved and particularly F.F.P. can be controlled in a desired shapefrom ellipse to true circle, so that various laser devices havingdiverse characteristics can be provided. The stripe ridge is not limitedto the normal mesa configuration shown in FIGS. 1 and 3 as describedabove, and may be formed in inverted mesa configuration or in stripeshape having vertical side faces. That is, the ridge shape may bechanged according to the laser characteristic required.

[0085] Also in the semiconductor laser device of the present invention,the ridge may be buried by regrowing crystal on both sides of the ridgeafter forming the stripe ridges 201, 202 when constituting the firstwaveguide region C₁ and the second waveguide region C₂.

[0086] As described above, since the present invention assumes the ridgewaveguide structure having the stripe ridge, it is made possible notonly to achieve production at a lower cost but also to make laserdevices having diverse characteristics by arranging the first waveguideregion C₁ and the second waveguide region C₂ in various combinations inthe waveguide. For example, since it is made possible to control thebeam characteristic, satisfactory F.F.P. can be achieved without usingbeam correction lens or the like.

[0087] In the laser device of the present invention, the first andsecond stripe ridges 201, 202 provided in the first waveguide region C₁and the second waveguide region C₂ have such a configuration as shown inFIG. 1B and FIG. 1C.

[0088] The present invention is also applicable to devices other thanlaser oscillation device, for example end-face light emitting devicessuch as light emitting diode. The device having the constitution shownin FIG. 1 can be operated as a light emitting diode by driving thedevice below the threshold of oscillation, and a device which emitslight from an end face without laser oscillation can be obtained byinclining the waveguide from the direction which is perpendicular to theend face, rather than making the waveguide perpendicular to the endface.

[0089] [Laminate Structure]

[0090] Now the structure of the laminate consisting of the layer offirst conductivity type, the active layer and the layer of secondconductivity type provided in the semiconductor device of thisembodiment will be described in detail below.

[0091] In the semiconductor device of this embodiment, as shown in FIG.1, cladding layers 5, 7 are provided in the layer 1 of firstconductivity type and the layer 2 of second conductivity type,respectively, and light is confined in the direction of thickness bysandwiching the active layer 3 with the cladding layers 5, 7. Thus theoptical waveguide region is provided within the laminate where light isconfined in the width direction (perpendicular to the direction ofthickness and perpendicular to the direction of resonance) by means ofridge and also light is confined in the direction of thickness by meansof the cladding layers 5, 7. In the semiconductor laser device of thepresent invention, various kinds of semiconductor material known in theprior art can be used such as those based on, for example, GaAlAs,InGaAsP and GaAlInN.

[0092] In the semiconductor laser device of the present invention, thestripe waveguide region is formed in correspondence to the ridge in theactive layer between the layer of the first conductivity type and thelayer of the second conductivity type, and in the vicinity thereof,while the longitudinal direction of the stripe and the direction oflight propagation are substantially identical. That is, while the stripewaveguide region is constituted mainly from the active layer in whichlight is confined, part of light is guided while spreading in thevicinity thereof, and therefore a guide layer may be formed between theactive layer and the cladding layer so that the region including theguide layer is used as the optical waveguide layer.

[0093] [Second Waveguide Region C₂]

[0094] The second waveguide region C₂ of the present invention is aregion provided as the effective refractive index type waveguide in thewaveguide of the semiconductor laser device. Specifically, the striperidge 201 is formed in the layer 2 of second conductivity type 2 locatedon the active layer 3 of the laminate, and the stripe waveguide regionis formed by providing effective difference in refractive index in thedirection of plane (width direction) of the active layer.

[0095] In a laser device of effective refractive index type of the priorart in which the waveguide consists of the second waveguide region C₂only, the stripe ridge 202 is formed by etching using a mask 20 afterforming the semiconductor layers as shown in FIG. 2. Since the striperidge 202 is formed by etching to such a depth that does not reach theactive layer thereby to provide the effective difference in refractiveindex in the active layer (waveguide layer), characteristics of thedevice vary significantly depending on the width Sw of the stripe,height of the ridge (depth of stripe) Sh₁ and distance Sh₂ between thesurface exposed by etching and the top plane of the active layer asshown in FIG. 2B. These factors cause serious variations in the devicecharacteristics during production thereof. That is, the variations inthe device characteristics are caused directly by error Hd in the heightof the ridge (depth of stripe) and error Wd in the width of the striperelated to the accuracy of etching shown in FIG. 2C and FIG. 2D. This isbecause the waveguide region formed in the active layer (waveguidelayer) is provided by making use of the effective difference inrefractive index corresponding to the ridge 202 by means of the striperidge 202 provided in the active layer (waveguide layer), and thereforethe configuration of the ridge has a significant influence on theeffective difference in refractive index. The error Hd in the height ofthe ridge is also the error in the distance between the surface exposedby etching and the top plane of the active layer. When the distance Sh₂between the top plane of the active layer and the surface exposed byetching is too large, the effective difference in refractive indexbecomes smaller resulting in significant influences on the devicecharacteristics such as insufficient confinement of light. As describedabove, since the effective refractive index is dependent on the distanceSh₂ between the top plane of the active layer and the surface exposed byetching, variations in the distance cause variations in the effectiverefractive index.

[0096]FIGS. 10, 11 and 12 show the ratio of products which pass theetching depth inspection, drive current and service life for the laserdevice of the effective refractive index type of the prior art. As willbe understood from the drawings, characteristics of the laser device arevery sensitive to the depth of etching.

[0097] In the laser device of the present invention, since the secondwaveguide region C₂ formed by etching to such a depth that does notreach the active layer is provided as a part of the waveguide, theactive layer is prevented from being damaged by etching in the secondwaveguide region C₂, and therefore reliability of the device can beimproved. In the case of a material which undergoes significant devicecharacteristics when the active layer is exposed to the atmosphere,providing the second waveguide region C₂ makes it possible to restrictthe reliability of the device from deteriorating.

[0098] [First Waveguide Region C₁]

[0099] According to the present invention, laser devices of variouscharacteristics can be easily made by forming the first waveguide regionC₁ in addition to the second waveguide region C₂ as the stripe waveguideregion, as described previously. This is an effect brought about by theexcellent controllability of the transverse mode of the first waveguideregion C₁ which is made by forming the stripe ridge 201 that includesportions of the active layer and the layer 1 of the first conductivitytype in the laminate structure.

[0100] In the first waveguide region C₁, since light is confined bymeans of the actual difference in the refractive index between theactive layer and the regions located on both sides thereof by limitingthe width of the active layer by the first ridge, it is made possible toconfine light more effectively.

[0101] Thus it is made possible to surely suppress the unnecessarytransverse mode of oscillation and control the transverse mode moreeffectively.

[0102] According to the present invention, as described above, byproviding the first waveguide region C₁ having excellent controllabilityof transverse mode in a part of the waveguide region, unnecessarytransverse mode of oscillation in the first waveguide region C₁ issuppressed thereby improving the controllability of transverse mode ofthe entire device, and it is made possible to easily obtain laserdevices of various beam characteristics.

[0103] With the laser device of the present invention, laser beam of adesired configuration can be easily achieved by forming the firstwaveguide region C₁ on one end so as to include the resonance end faceof the laser resonator. In other words, it is preferable to form thelaser resonance end face 4 so as to correspond to the end face of thefirst waveguide region C₁ as shown in FIG. 3B, FIG. 4A and FIG. 4B. Thisis because, when the region in the vicinity of the resonance end face isturned into the first waveguide region C₁, the transverse mode of lightcan be controlled before and after reflection on the resonance end face,so that the control of the transverse mode functions more effectively inthe waveguide than in a case of providing in other region

[0104] Also according to the present invention, the laser device havingexcellent beam characteristics such as F.F.P. and laser beam aspectratio can be obtained by using the end face of the first waveguideregion C₁ as the laser resonance end face and using the laser resonanceend face as the light emitting plane. This is because, with thisconstitution, by providing the first waveguide region C₁ on the laserbeam emitting plane, it is made easier to control the transverse mode inthe first waveguide region C₁, so that the beam characteristic can beeasily controlled. In case the first waveguide region C₁ is constitutedfrom the first stripe ridge 201 as shown in FIGS. 3, 4, the transversemode can be easily controlled and the desired beam characteristic can beobtained with high accuracy by adjusting the width of stripe of thefirst ridge 201.

[0105] Length of the first waveguide region C₁ provided on the lightemitting plane may be at least one wavelength of the light emitted bythe laser, though a length of several times the wavelength is preferablein consideration of the function to control the transverse oscillationmode in which case desired beam characteristic can be achieved.

[0106] Specifically, it is preferable to form the first waveguide regionC₁ with a length of 1 μm or longer, which enables satisfactory controlof the transverse oscillation mode. When consideration is given to themanufacturing process, it is preferable to form the first waveguideregion with a length of 5 μm or longer since the stripe ridge 201 can beformed with better accuracy with this length.

[0107] Width of the active layer (length in the direction perpendicularto the resonator direction) may be 10 μm, preferably 50 μm or longer andmore preferably 100 μm or longer. In such a constitution as a pair ofpositive and negative electrodes oppose each other via a substrate,width of the active layer becomes equivalent to the chip width. In sucha constitution as a pair of positive and negative electrodes is providedon the same side of a substrate, a surface is exposed to form electrodesin the layer of the first conductivity type thereon, the length is thechip width minus the width of the portion which is removed to form theexposed surface.

[0108] [Constitution of Waveguide]

[0109] The laser device of the present invention is characterized by thestripe waveguide region having at least the first waveguide region C₁and the second waveguide region C₂, so that the characteristics of thelaser devices can be easily modified by changing the arrangement of thewaveguide regions in the resonator without modification of thecomplicated device design. Specifically, by disposing the firstwaveguide region C₁ on the resonance end face as described above, beamcharacteristic can be easily controlled and desired characteristic canbe easily obtained. Also by setting the proportion of the waveguideoccupied by the first waveguide region C₁ wherein the side face of theactive layer is exposed smaller than that of the second waveguide regionC₂, the laser device of higher reliability can be obtained. This isbecause the proportion of the active layer which is not damaged byetching can be increased by providing more second waveguide region C₂ inthe waveguide. As a result, service life of the device can be elongatedand variations in the service life among the devices can be decreased.

[0110] While the laser device of the present invention has at least thefirst waveguide region C₁ and the second waveguide region C₂ as thewaveguide, a waveguide region of a configuration other than the firstwaveguide region C₁ and the second waveguide region C₂ may also beprovided. For example, a flat surface 203 formed to incline between thefirst waveguide region C₁ and the second waveguide region C₂ as shown inFIG. 4A may be used. Thus in addition to the first waveguide region C₁and the second waveguide region C₂, a waveguide different from these maybe provided. Further, the first waveguide region C₁ and the secondwaveguide region C₂ may be provided, one each, in the waveguide or maybe provided in plurality as shown in FIG. 4B. Also nothing may beprovided between the first waveguide region C₁ and the second waveguideregion C₂ as shown in FIG. 3 and FIG. 4B, or an inclination reverse tothat shown in FIG. 4A may be provided so that the first waveguide regionC₁ and the second waveguide region C₂ partially overlap each other.

[0111] The laser device of the present invention may also have such aconstitution as a third waveguide region C₃ is formed in addition to thefirst waveguide region C₁ and the second waveguide region C₂ so that theside face of the active layer (side face of waveguide layer) 204 isinclined against the resonator direction. FIG. 13A is a schematicperspective view of the device structure, and FIG. 13B is a sectionalview showing a portion near the junction between the upper claddinglayer 7 and the active layer 3. In this constitution, the thirdwaveguide region C₃ shares the stripe ridge 202 on the upper claddinglayer 7 with the second waveguide region C₂, and the end face (sideface) 204 of the active layer (waveguide layer) is provided in aninclined configuration. In the laser device having the constitutiondescribed above, light guided by the side face 204 can be reflectedcompletely by adjusting the angle α between the resonator direction AAand the direction BB of the active layer side face, as shown in FIG.13B, thus making it possible to guide the light into the first waveguideregion C₁ first waveguide region C₁ striped configuration. Specifically,when the angle α is 70° or less, the incident angle of light in thedirection AA of the resonator on the end face 204 can be set to 20° orgreater so that total reflection without loss can be achieved. Thus theangle α can be set in a range from 0 to 70° according to theapplication. For example, when the angle α is 20° or less, the incidentangle of light in the direction AA of the resonator on the end face 204can be set to 70° or greater, in which case total reflection withoutloss can be achieved. In the second waveguide region C₂, while thestripe waveguide region is formed by making use of the effectivedifference in refractive index in the active layer (waveguide layer),there exists light tat is guided outside of the waveguide region andthis portion of light is reflected on the end face of the secondwaveguide region C₂.

[0112] In this case, when the loss in light increases, output powerdecreases leading to a deterioration in the current-optical output slopeefficiency. When the second waveguide region C₂ is wider than the firstwaveguide region C₁, providing the third waveguide region C₃ between thesecond waveguide region C₂ and the first waveguide region C₁ decreasesthe light loss, thus making it possible to guide the lightsatisfactorily in the junction with the first waveguide region C₁ asshown in FIG. 13.

[0113] In the laser device of the present invention, the stripe ridges201, 202 that constitute the first waveguide region C₁ and the secondwaveguide region C₂ may have different widths. Beams of different aspectratios can be achieved by changing the stripe width. Therefore, thefirst ridge and the second ridge can be formed with widths appropriatefor the application in the laser device of the present invention. Whilea small width requires an accuracy in the control of the width, it alsoachieves such characteristics as FFP near true circle or it is madepossible to change the spread of the beam in correspondence to thewidth. Specifically, when the width is decreased gradually in a portion205 of the second waveguide region C₂ as shown in FIG. 15, for example,the stripe width in the junction with the first waveguide region C₁ canbe made equal to the stripe width S_(w2), thus making it possible toextract laser beam of various modes in correspondence to the width ofthe first waveguide region C₁. In FIG. 15, a portion where width of thesecond waveguide region C₂ is decreased gradually is shown as the thirdwaveguide region C₃.

[0114] In FIG. 15, in order to constitute the second waveguide regionC₂, the first ridge 202 having width S_(w1) larger than the stripe widthS_(w2) of the first ridge that constitutes the first waveguide region C₁is provided thereby to form a waveguide which undergoes less variationin the characteristic with a change in the effective refractive index.In the third waveguide region C₃, at the same time, a region 205 havingstripe width inclined in the waveguide is provided so as to join thewaveguide regions of different stripe widths smoothly, therebyminimizing the loss in the junction. The ridge for constituting thethird waveguide region C₃ may be provided above the active layer asshown in the drawing, or at a depth reaching the layer of firstconductivity by etching similarly to the first waveguide region C₁, orat a position located inbetween.

[0115] The stripe ridge for constituting the first and second waveguideregions of the present invention may be formed in variousconfigurations, for example in a tapered configuration where the stripewidth varies along the direction of stripe (longitudinal direction ofstripe). Specifically, as exemplified by the first embodiment or shownin FIG. 15, in the waveguide structure having the first waveguide regionC₁ disposed at the light emitting end, the second waveguide region C₂having larger stripe width may be formed in such a configuration thatthe stripe width decreases toward the narrower first waveguide regionC₁, thereby decreasing the light waveguide to the junction of bothportions. Such a tapered stripe may be formed partially as the stripe ofeach waveguide region, or formed in a tapered configuration over theentire length of the stripe, or in such a configuration as a pluralityof tapered stripes having width which decreases toward both endsthereof.

[0116] [Stripe in Nitride Semiconductor]

[0117] The semiconductor laser device of the present inventionconstituted from the semiconductors of the first conductivity type andthe second conductivity type and the active layer made of nitridesemiconductor will be described below.

[0118] The nitride semiconductor used in the laser device of the presentinvention may be GaN, AlN or InN, or a mixed crystal thereof, namely theGroup III-V nitride semiconductor (In_(b)Al_(d)Ga_(1−b−d)N, 0≦b, 0≦d,b+d≦1). Mixed crystals made by using B as the Group III element or bypartially replacing N of the Group V element with As or P may also beused. The nitride semiconductor can be made to have a desiredconductivity type by adding an impurity of appropriate conductivitytype. As an n-type impurity used in the nitride semiconductor, the GroupIV or VI elements such as Si, Ge, Sn, S, O, Ti and Zr may be used, whileSi, Ge or Sn is preferable and most preferably Si is used. As the p-typeimpurity, Be, Zn, Mn, Cr, Mg, Ca or the like may be used, and Mg ispreferably used. As a specific example of the laser device of thepresent invention, a nitride semiconductor laser device will bedescribed below. The nitride semiconductor laser device herein refers toa laser device where nitride semiconductor is used in any of the layerof the first conductivity type, the active layer and the layer of thesecond conductivity type which constitute the laminate, or preferably inall of these layers. For example, cladding layers made of nitridesemiconductor are formed in the layer of the first conductivity type andthe layer of the second conductivity type while the active layer isformed between the two cladding layers thereby forming the waveguide.More specifically, the layer of the first conductivity type includes an-type nitride semiconductor layer and the layer of the secondconductivity type includes a p-type nitride semiconductor layer, whilethe active layer includes nitride semiconductor laser which includes In.

[0119] (Active Layer)

[0120] According to the present invention, when the semiconductor laserdevice of the present invention is constituted from nitridesemiconductor, providing the nitride semiconductor layer which includesIn in the active layer makes it possible to emit laser beam over a rangeof wavelengths from blue to red light in the ultraviolet and visibleregions. While the laser device may suffer very serious damage on thenitride semiconductor laser including In when the active layer isexposed to the atmosphere, such a damage to the device can be minimizedaccording to the present invention since the device includes the secondwaveguide region C₂ which is constituted from the first ridge 202provided at such a depth that does not reach the active layer. This isbecause the low melting point of In makes the nitride semiconductorwhich includes In easy to decompose and evaporate and prone to damageduring etching, and makes it difficult to maintain the crystallinityduring the process following the exposure of the active layer, thusresulting in a shorter service life of the device.

[0121]FIG. 12 shows the relationship between the depth of etching forforming the stripe ridge and the device life. As will be seen from thedrawing, device life decreases dramatically when etching process reachesthe active layer which has the nitride semiconductor which includes In,and exposure of the active layer leads to serious deterioration of thereliability of the laser device.

[0122] Since the laser device of the present invention is provided withthe first waveguide region C₁ and the second waveguide region C₂ as thewaveguide, the laser device of excellent reliability can be achievedeven in a nitride semiconductor laser device which would otherwiseundergo deterioration in the characteristics when the active layer isexposed to the atmosphere. This is because the first ridge 201 providedfor the constitution of the first waveguide region C₁ constitutes only apart of the waveguide so that reliability of the device can be preventedfrom deteriorating. When length of the resonator is set to about 650 μmand length of the first ridge 201 provided for the constitution of thefirst waveguide region C₁ is set to 10 μm in the nitride semiconductorlaser device of the present invention, for example, it is confirmed thatthe device does not undergo deterioration in reliability due to theactive layer being exposed in the first ridge, and service life ofseveral thousands of hours is ensured with operation of 5 mW in outputpower.

[0123] In the nitride semiconductor laser device of the presentinvention, width of the stripe of the ridge that constitutes the firstwaveguide region C₁ or the second waveguide region C₂ is preferably setin a range from 0.5 to 4 μm, or more preferably in a range from 1 to 3μm in which case it is made possible to oscillate in stable transversemode wit the fundamental (single) mode. When stripe width of the ridgeis less than 1 μm, it becomes difficult to form the ridge, while widthof 3 μm or greater may cause multi-mode oscillation in the transversemode depending on the wavelength of laser oscillation, and width of 4 μmor greater may make it impossible to achieve stable transverse mode.According to the present invention, controlling the width in a rangefrom 1.2 to 2 μm makes it possible to further effectively stabilize thetransverse mode in a high optical output power (effectively suppress theoscillation in unnecessary transverse mode). According to the presentinvention, while it is good for the stripe width of the ridge wheneither of the first waveguide region C₁ or the second waveguide regionC₂ is within the range described above, it is preferable to set thestripe ridge 201 of the first waveguide region C₁ within the rangedescribed above in case the first waveguide region C₁ is provided on thelight emitting side of the resonator plane. Also the present inventionis not limited to such a narrow stripe structure as described above, andmay be applied to a stripe having a width of 5 μm or greater. Also insuch a constitution as the first waveguide region C₁ is disposed on theend of the waveguide, the stripe width of the second waveguide region C₂can be set relatively freely for the control of the laser beamcharacteristic by means of mainly the first waveguide region C₁.

[0124] In the nitride semiconductor laser device of the presentinvention, when the end face of the first waveguide region C₁ is used asthe resonance end face (light emitting plane), the laser device havingexcellent controllability of transverse mode, F.F.P. aspect ratio anddevice reliability can be obtained. This is because, as describedpreviously, light emitted from the laser device can be controlledimmediately before the emission by etching deeper than the active layerthereby providing the first waveguide region C₁ on the light emittingside of the resonator plane, thereby making it possible to obtain laserbeams of various shapes and spot sizes.

[0125] The active layer may have quantum well structure and, in thatcase, may be either single quantum well or multiple quantum wellstructure. High power laser device and end face light emitting device ofexcellent light emitting efficiency can be made by employing the quantumwell structure. The second stripe ridge 202 provided for constitutingthe second waveguide region C₂ is formed by etching to such a depth thatdoes not reach the active layer. In this specification, the statementthat the second stripe ridge 202 is located above the active layer meansthat the formation by etching to such a depth that does not reach theactive layer. That is, the second stripe ridge 202 that constitutes thesecond waveguide region C₂ is positioned above the interface between theactive layer and the layer formed in contact and above thereof.

[0126] The active layer of the nitride semiconductor is preferably thenitride semiconductor which includes In as described above, andspecifically a nitride semiconductor represented byAl_(x)In_(y)Ga_(1−x−y)N (0≦x≦1, 0<y≦1, x+y≦1) is preferably used. Inthis case, the nitride semiconductor described here is preferably usedas the well layer in the active layer of quantum well structure. In thewavelength region (from 380 nm to 550 nm) ranging from near ultravioletto visible green light, In_(y)Ga_(1−y)N (0<y0) is preferably used. Alsoin a region of longer wavelengths (red), In_(y)Ga_(1−y)N (0<y0) can beused similarly and, at this time, laser beam of a desired wavelength canbe emitted by changing the proportion y of mixing In. In a region ofwavelengths shorter than 380 nm, since the wavelength which correspondsto the forbidding band width of GaN is 365 nm, band gap energy nearlyequal to or greater than that of GaN is required, and thereforeAl_(x)In_(y)Gal_(1−x−y)N (0<x≦1, 0<y≦1, x+y≦1) is used.

[0127] In case the active layer is formed in the quantum well structure,thickness of the well layer is in a range from 10 Å to 300 Å, andpreferably in a range from 20 Å to 200 Å, which allows it to decrease Vfand the threshold current density. When the crystal is taken intoconsideration, a layer of relatively homogeneous quality without muchvariations in the thickness can be obtained when the thickness is 20 Åor greater, and the crystal can be grown while minimizing the generationof crystal defects by limiting the thickness within 200 Å. There is nolimitation on the number of well layers in the active layer, which maybe 1 or more. When four or more active layers with larger thickness oflayers constituting the active layer, total thickness of the activelayers becomes too large and the value of Vf increases. Therefore, it isdesirable to restrict the thickness of the well layer within 100 Åthereby to restrain the thickness of the active layer. In the case of LDand LED of high output power, setting the number of well layers in arange from 1 to 3 makes it possible to obtained devices of high lightemission efficiency and is desirable.

[0128] The well layer may also be doped or undoped with p- or n-typeimpurity (acceptor or donor). When nitride semiconductor which includesIn is used as the well layer, however, increase in the concentration ofn-type impurity leads to lower crystallinity and therefore it ispreferable to restrict the concentration of n-type impurity thereby toachieve make the well layer of good crystallinity. Specifically, inorder to achieve best crystallinity, the well layer is preferably grownwithout doping with the n-type impurity concentration kept within5×10¹⁶/cm³. The state of the n-type impurity concentration kept within5×10¹⁶/cm³ means an extremely low level of concentration of n-typeimpurity, and the well layer can be regarded as including substantiallyno n-type impurity. When the well layer is doped with n-type impurity,controlling the n-type impurity concentration within a range from1×10¹⁸/cm³ to 5×10¹⁶/cm³ makes it possible to suppress the degradationof crystallinity and increase the carrier concentration.

[0129] There is no limitation to the composition of the barrier layer,and nitride semiconductor similar to that of the well layer can be used.Specifically, a nitride semiconductor which includes In such as InGaNhaving lower proportion of In than the well layer, or a nitridesemiconductor which includes Al such as GaN, AlGaN may be used. Band gapenergy of the barrier layer must be higher than that of the well layer.Specific composition may be In_(β)Gal_(1−β)N (0≦β<1, α>β), GaN,Al_(γ)Ga_(1−γ)N (0<γ≦1), and preferably In_(β)Gal_(1−β)N (0≦β<1, α>β),GaN which makes it possible to form the barrier layer of goodcrystallinity. This is because growing a well layer made of a nitridesemiconductor which includes In directly on a nitride semiconductorwhich includes Al such as AlGaN leads to lower crystallinity, eventuallyresulting in impeded function of the well layer. When Al_(γ)Ga_(1−γ)N(0<γ≦1) is used in the barrier layer, the above problem can be avoidedby providing the barrier layer which includes Al on the well layer andproviding a multi-layered barrier layer comprising In_(β)Ga_(1−β)N(0≦β<1, α>β), GaN below the well layer. Thus in the multiple quantumwell structure, the barrier layer sandwiched between the active layersis not limited to a single layer (well layer/barrier layer/well layer),and two or more barrier layers of different compositions and/or impurityconcentrations may be stacked such as well layer/barrier layer (1)/barrier layer (2)/well layer. Letter α represents the proportion of Inin the well layer, and it is preferable to make the proportion of In βin the barrier layer lower than that of the well layer as α>β.

[0130] The barrier layer may be doped or undoped with the n-typeimpurity, but preferably doped with the n-type impurity. When doped, then-type impurity concentration in the barrier layer is preferably5×10¹⁶/cm³ or higher and lower than 1×10²⁰/cm³. In the case of LED whichis not required to have a high output power, for example, the n-typeimpurity concentration is preferably in a range from 5×10¹⁶/cm³ to2×10¹⁸/cm³. For LED of higher output power and LD, it is preferable todope in a range from 5×10¹⁷/cm³ to 1×10²⁰/cm³ and more preferably in arange from 1×10¹⁸/cm³ to 5×10¹⁹/cm³. When doping to such a highconcentration, it is preferable to grow the well layer without doping orwith substantially no n-type impurity included. The reason for then-type impurity concentration being different among the regular LED, thehigh-power LED and the high-power LD (output power in a range from 5 to100 mW) is that a device of high output power requires higher carrierconcentration in order to drive with larger current for higher outputpower. Doping in the range described above, as described above, it ismade possible to inject the carrier to a high concentration with goodcrystallinity.

[0131] In the case of a nitride semiconductor device such as lower-powerLD, LED or the like, in contrast, a part of the barrier layer of theactive layer may be doped with the n-type impurity or the entire barrierlayers may be formed with substantially no n-type impurity included.When doping with the n-type impurity, all the barrier layers of theactive layer may be doped or a part of the barrier layers may be doped.When part of the barrier layers is doped with the n-type impurity, it ispreferable to dope the barrier layer which is disposed on the n-typelayer side in the active layer. Specifically, when the barrier layer Bn(n=1, 2, 3 . . . ) which is nth layer from the n-type layer side,electrons are effectively injected into the active layer and a devicehaving excellent light emission efficiency and quantum efficiency can bemade. This also applies to the well layer, as well as the barrier layer.When both the barrier layer and the active layer are doped, the effectdescribed above can be achieved by doping the barrier layer Bn (n=1, 2,3 . . . ) which is nth layer from the n-type layer side and the mth welllayer Wm (m=1, 2, 3 . . . ), namely doping the layer nearer to then-type layer first.

[0132] While there is no limitation to the thickness of the barrierlayer, the thickness is preferably not larger than 500 Å, and morespecifically from 10 to 300 Å similarly to the active layer.

[0133] In the nitride semiconductor laser device of the presentinvention, it is preferable that the laminate structure includes then-type nitride semiconductor layer for the layer of first conductivitytype and the p-type nitride semiconductor for the layer of secondconductivity type. Specifically, the n-type cladding layer and thep-type cladding layer are provided in the layers of the respectivetypes, thereby to form the waveguide. At this time, a guide layer and/oran electron confinement layer may be formed between the cladding layersand the active layer.

[0134] (p-type Cladding Layer)

[0135] In the nitride semiconductor laser device of the presentinvention, it is preferable to provide the p-type cladding layer whichincludes the p-type nitride semiconductor (first p-type nitridesemiconductor) as the layer of second conductivity type or the layer offirst conductivity type. In this case, the waveguide is formed in thelaminate structure by providing the n-type cladding layer which includesthe n-type nitride semiconductor layer in the layer of the conductivitytype different from that of the layer wherein the p-type cladding layeris provided. The nitride semiconductor used in the p-type cladding layeris required only to have a difference in the refractive index largeenough to confine light, and nitride semiconductor layer which includesAl is preferably used. This layer may be either a single layer or amulti-layered film. Specifically, a super lattice structure having AlGaNand GaN stacked one on another achieves better crystallinity and istherefore preferable. This layer may be either doped with p-typeimpurity or not doped. For a laser device oscillating at a longwavelength in a range from 430 to 550 nm, the cladding layer ispreferably made of GaN doped with p-type impurity. While there is nolimitation to the film thickness, thickness in a range from 100 Å to 2μm, or more preferably from 500 Å to 1 μm makes the film functionsatisfactorily as the light confinement layer.

[0136] Also according to the present invention, the electron confinementlayer and/or the optical guide layer to be described later may beprovided between the active layer and the p-type cladding layer. Whenproviding the optical guide layer, it is preferable provide the opticalguide layer also between the n-type cladding layer and the active layer,in such a structure as the active layer is sandwiched by optical guidelayers. This creates SCH structure in which light can be confined by thecladding layer by making the proportion of Al content higher in thecladding layer than in the guide layer thereby providing a difference inrefractive index. In case the cladding layer and the guide layer areformed in multi-layered structure, proportion of Al content isdetermined by the mean proportion of Al.

[0137] (p-type Electron Confinement Layer)

[0138] The p-type electron confinement layer which is provided betweenthe active layer and the p-type cladding layer, or preferably betweenthe active layer and the p-type optical guide layer also function toconfine the carrier in the active layer thus making it easier tooscillate by reducing the threshold current, and is made of AlGaN.Particularly more effective electron confinement can be achieved byproviding the p-type cladding layer and the p-type electron confinementlayer in the layer of second conductivity type. When AlGaN is used forthe p-type electron confinement layer, while the above mentionedfunction can be reliably achieved by doping with the p-type impurity,carrier confining function can also be achieved even without doping.Minimum film thickness is 10 Å and preferably 20 Å. The above mentionedfunction will be achieved satisfactorily by forming the film to athickness within 500 Å and setting the value of x in formulaAl_(x)Ga_(1−x)N to 0 or larger, preferably 0.2 or larger. The n-typecarrier confinement layer may also be provided on the m-type layer sidefor confining the holes within the active layer. Confinement of holescan be done without making such an offset (difference in the band gapfrom the active layer) as in the case of electron confinement.Specifically, a composition similar to that of the p-type electronconfinement layer may be used. In order to achieve good crystallinity,this layer may be formed from a nitride semiconductor layer which doesnot includes Al, and a composition similar to that of the barrier layerof the active layer may be used. In this case, it is preferable todispose the n-type barrier layer which confines the carrier nearest tothe n-type layer in the active layer, or within the n-type layer incontact with the active layer. Thus by providing the p-type and n-typecarrier confinement layers in contact with the active layer, the carriercan be injected effectively into the active layer or into the welllayer. In another form, a layer which makes contact with the p-type orn-type layer in the active layer can be used as the carrier confinementlayer.

[0139] [p-type Guide Layer]

[0140] According to the present invention, good waveguide can be formedfrom nitride semiconductor by providing the guide layer which sandwichesthe active layer at a position inside of the cladding layer therebyforming the optical waveguide. In this case, thickness of the waveguide(the active layer and the guide layers on both sides thereof) is set towithin 6000 Å for suppressing abrupt increase in the oscillationthreshold current. Preferably the thickness is within 4500 Å to makecontinuous oscillation possible with long service life at a restrictedthreshold current in the fundamental mode. Both guide layers arepreferably formed to substantially the same thickness in a range from100 Å to 1 μm, more preferably in a range from 500 Å to 2000 Å in orderto form good optical waveguide. The guide layer is made of nitridesemiconductor, while it suffices to have a band gap energy sufficient toform the waveguide compared to the cladding layer to be provided on theoutside thereof, and may be either a single film or a multi-layeredfilm. Good waveguide can be formed by making the optical guide layerhaving a band gap energy equal to or greater than that of the activelayer. In the case of quantum well structure, band gap energy is madegreater than that of the well layer, and preferably greater than that ofthe barrier layer. Further, good optical waveguide can be formed byproviding a band gap energy for about 10 nm or larger than thewavelength of light emitted in the active layer in the optical guidelayer.

[0141] For the p-type guide layer, it is preferable to use undoped GaNin the range of oscillation wavelengths from 370 to 470 nm, and use amulti-layered structure of InGaN/GaN in a range of relatively longwavelengths (450 μm and over). This makes it possible to increase therefractive index in the waveguide constituted from the active layer andthe optical guide layer, thereby increasing the difference in therefractive index from the cladding layer. In a range of shorterwavelengths within 370 nm, nitride semiconductor which includes Al ispreferably used since the absorption edge is at 365 nm. Specifically,Al_(x)Ga_(1−x)N (0<x<1) is preferably used to form a multi-layered filmmade of AlGaN/GaN, multi-layered film made by alternate stacking thereofor a super lattice multi-layered film in which each layer has superlattice structure. Constitution of the n-type guide layer is similar tothat of the p-type guide layer. Satisfactory waveguide can be can bemade by using GaN, InGaN in consideration of the energy band gap of theactive layer, and forming multi-layered film comprising InGaN and GaNstacked alternately with the proportion of In content being decreasedtoward the active layer.

[0142] (n-type Cladding Layer)

[0143] In the nitride semiconductor laser device of the presentinvention, nitride semiconductor used in the n-type cladding layer isrequired only to have a difference in the refractive index large enoughto confine light similarly to the p-type cladding layer, and a nitridesemiconductor layer which includes Al is preferably used. This layer maybe either a single layer or a multi-layered film. Specifically, a superlattice structure having AlGaN and GaN stacked one on another. Then-type cladding layer functions as the carrier confinement layer and thelight confinement layer. In case multi-layered structure is employed, itis preferable to grow nitride semiconductor layer including Al,specifically AlGaN as described previously. Further, this layer may beeither doped with n-type impurity or not doped, and also one of theconstituting layers may be doped. For a laser device oscillating at along wavelength in a range from 430 to 550 nm, the cladding layer ispreferably made of GaN doped with n-type impurity. While there is nolimitation to the film thickness, similarly to the case of the p-typecladding layer, thickness in a range from 100 Å to 2 μm, or morepreferably from 500 Å to 1 μm makes the film function satisfactorily asthe light confinement layer.

[0144] In the nitride semiconductor laser device, good insulation can beachieved by locating the position, where the stripe ridge is formed,within the nitride semiconductor layer which includes Al and providingan insulation film on the exposed nitride semiconductor surface and onthe side face of the ridge. A laser device without leak current can alsobe made by providing electrodes on the insulation film. This is becausealmost no material exists that can achieve good ohmic contact in thenitride semiconductor layer which includes Al, and good insulationwithout leak current can be achieved by forming the insulation film andelectrode on the semiconductor surface. When the electrode is providedon the nitride semiconductor layer which does not include Al, incontrast, ohmic contact can be easily formed between the electrode andthe nitride semiconductor. When the electrode is formed on the nitridesemiconductor layer which does not include Al via the insulation film,microscopic pores in the insulation film cause leakage depending on thefilm quality of the insulation film and the electrode. In order to solvethis problem, it is necessary to form the insulation film having athickness sufficient to provide the required level of insulation or todesign the shape and position of the electrode so as not to overlap thesemiconductor surface, thus imposing a significant restraint on thedesign of the laser device constitution. It is important where toprovide the ridge, because the surface of the nitride semiconductor onboth sides of the ridge exposed when forming the ridge has far greaterarea than the side face of the ridge, and satisfactory insulation can besecured in this surface. Thus a laser device having a high degree offreedom in the design can be made where electrodes of variousconfigurations can be applied and the location of forming the electrodecan be determined relatively freely, which is very advantageous informing the ridge. For the nitride semiconductor layer which includesAl, AlGaN or the super lattice multi-layered structure of AlGaN/GaNdescribed above is preferably used.

[0145] The first ridge 201 and the second stripe ridge 202 of stripedconfiguration provided as the first waveguide region C₁ and the secondwaveguide region C₂ are formed by removing both sides of each ridge asshown in FIGS. 1B and 1C. The ridge 202 is provided on the uppercladding layer 7 and the surface of the upper cladding layer 7 exposedin a region other than the ridge determines the depth of etching.

[0146] [Electrode]

[0147] The laser device of the present invention is not limited to theelectrode configuration provided on the stripe ridge and the secondridge. As shown in FIG. 1 and FIG. 7, for example, the electrode may beformed on almost the entire surface of the first stripe ridge 201 andthe second stripe ridge 202 provided as the first waveguide region C₁and the second waveguide region C₂. Also the electrode may be providedon the second waveguide region C₂ only thereby injecting the carrierinto the second waveguide region C₂ with preference. On the contrary,the electrode may be provided on the first waveguide region C₁ only,with the waveguide being functionally separated in the direction ofresonator.

[0148] [Insulation Film]

[0149] In the laser device of the present invention, in case a part ofthe laminate is removed and a stripe ridge is provided to form theresonator, it is preferable to form the insulation film on the side faceof the stripe and on the plane (surface whereon the ridge is provided)on both sides of the ridge which continues thereto. For example, afterthe stripe ridge shown in FIG. 1 is provided, the insulation film isprovided in such a way as to extend from the side face of the ridge tothe surfaces on both sides of the ridge.

[0150] In case nitride semiconductor is used in the laser device of thepresent invention, it is preferable to provide a second protective film162 as an insulation film as shown in FIGS. 7, 8, 9.

[0151] For the second protective film, a material other than SiO₂,preferably an oxide which includes at least one kind of element selectedfrom among the group consisting of Ti, V, Zr, Nb, Hf and Ta, or at leastone of SiN, BN, SiC and AlN is used and, among these, it is particularlypreferable to use Zr or Hf, or BN, SiC. While some of these materialsare slightly soluble to hydrofluoric acid, use of these materials as theinsulation layer of the laser device will achieve reliability fairlyhigher than SiO₂ as a buried layer. In the case of a thin film made ofan oxide which is formed in vapor phase such as PVD or CVD, since it isgenerally difficult for the element and oxygen to reactstoichiometrically to form the oxide, reliability tends to be lower forthe insulation of the thin film of oxide. In contrast, oxides of theelement selected in the present invention formed by PVD or CVD, and BN,SiC or AlN have higher reliability of insulation property than Si oxide.Moreover, when an oxide having a refractive index lower than that of thenitride semiconductor (for example, one other than SiC) is selected, aburied layer of laser device can be favorably formed. Further, when thefirst protective film 161 is formed from Si oxide, since the Si oxidecan be removed using hydrofluoric acid, the second protective film 162having uniform thickness can be formed on the surface except for the topsurface of the ridge as shown in FIG. 7C, by forming the firstprotective film 161 only on the top surface of the ridge as shown inFIG. 7B, forming the second protective film 162 continuously on thefirst protective film 161, the side faces of the ridge and the surfaceson both sides of the ridge (etching stopper layer), and selectivelyremoving the first protective film 161.

[0152] Thickness of the second protective film is in a range from 500 Åto 1 μm, and preferably in a range from 1000 Å to 5000 Å. When thethickness is less than 500 Å, sufficient insulation cannot be achievedwhen forming the electrode. When thicker than 1 μm, uniformity of theprotective film cannot be achieved and good insulation film cannot beobtained. When the thickness is in the preferred range described above,a uniform film having a favorable difference in refractive index fromthat of the ridge can be formed on the side face of the ridge.

[0153] The second protective film can also be formed by means of buriedlayer of nitride semiconductor. In the case of semi-insulating, i-typenitride semiconductor, type of conductivity opposite to that of theridge of the waveguide region, for example in the second waveguideregion C₂ of the first embodiment, a buried layer made of n-type nitridesemiconductor can be used as the second protective film. As a specificexample of buried layer, confinement of light in the transversedirection can be achieved by providing a difference in refractive indexfrom the ridge by means of a nitride semiconductor layer which includesAl such as AlGaN or achieving the function of current blocking layer,and good optical property of the laser device can be achieved byproviding a difference in the light absorption coefficient by means of anitride semiconductor laser which includes In. When a layer other thansemi-insulating, i-type layer is used for the buried layer, the secondwaveguide region may be a buried layer of the first conductivity typedifferent from the second conductivity type. In the first ridge thatconstitutes the first waveguide region, on the other hand, since thelayers of the first and second conductivity types are formed in stripeconfiguration on both sides of the active layer, a buried layer of thesecond conductivity type different from the first conductivity type isformed in the layer of the first conductivity type or in the regions onboth sides of the layer of the first conductivity type and the activelayer, while a buried layer of the first conductivity type differentfrom the second conductivity type is formed in the layer of the secondconductivity type or in the regions on both sides of the layer of thesecond conductivity type and the active layer. As described above, theburied layer may be formed in different constitutions in the firstwaveguide region and the second waveguide region. The buried layer isformed on a part of the stripe side face, or preferably oversubstantially the entire surface, similarly to the second protectivefilm. Moreover, when the buried layer is formed on the side face of theridge and the surface of the nitride semiconductor on both sides of theridge, better light confinement effect and current pinching effect canbe achieved. Such a constitution may also be employed as, after formingthe buried layer, a layer of nitride semiconductor is formed on theburied layer and/or the stripe and ridges constituting the waveguideregions are disposed in the device.

[0154] Length of the resonator of the nitride semiconductor laser deviceof the present invention may be in a range from 400 to 900 μm, in whichcase the drive current can be decreased by controlling the reflectanceof the mirrors on both ends.

[0155] [Manufacturing Method]

[0156] As described above, the nitride semiconductor laser device of thepresent invention can achieve good device characteristics. Further, thestripe waveguide region of the laser device of the present invention canbe made with a high accuracy and high yield of production, by formingthe stripes that make the first waveguide region C₁ and the secondwaveguide region C₂ in the process described below. The manufacturingmethod also makes it possible to manufacture the laser device havinghigh reliability. The manufacturing method will now be described indetail below.

[0157] As shown in FIGS. 8 and 9, when manufacturing a device having apair of positive and negative electrodes formed on the same side ofdifferent kind of substrate, in order to expose an n-type contact layerwhereon the negative electrode is to be formed as shown in FIG. 7,etching is done to that depth followed by etching to form the stripewaveguide region.

[0158] (Method 1 for Forming the Stripe Ridge)

[0159]FIG. 5 is a schematic perspective view showing a part of a waferwhereon device structure is formed from nitride semiconductor, forexplaining the process of forming the electrodes according to thepresent invention. FIG. 6 is a similar drawing for explaining anotherembodiment of the present invention. FIG. 7 shows a process afterforming the second protective film, FIG. 7B showing sectional view ofthe second waveguide region C₂ in FIG. 7A and FIG. 7C showing sectionalview of the second waveguide region C₂ in FIG. 7D. According to themanufacturing method of the present invention, as shown in FIG. 5A,after stacking the semiconductor layers that constitute the devicestructure, the first protective film 161 of stripe configuration isformed on a contact layer 8 in the layer of second conductivity type onthe top layer.

[0160] The first protective film 161 may be made of any material as longas it has a difference from the etching rate of the nitridesemiconductor, whether insulating or not. For example, Si oxide(including SiO₂), photoresist or the like is used, and such a materialthat is more soluble to an acid than the second protective film does ispreferably used in order to differentiate the solubility against thesecond protective film which will be formed later. Hydrofluoric acid ispreferably used for the acid, and accordingly Si oxide is preferablyused as the material soluble to hydrofluoric acid. Stripe width (W) ofthe first protective film is controlled within a range from 1 μm to 3μm. Stripe width of the first protective film 161 roughly corresponds tothe stripe width of the ridge that constitutes the waveguide region.

[0161]FIG. 5A shows the first protective film 161 being formed on thesurface of the laminate. That is, the first protective film 161 havingsuch a stripe configuration as shown in FIG. 5A is formed on the surfaceof the contact layer 8 by, after forming the second protective film oversubstantially the entire surface of the laminate, forming a mask of adesired shape on the surface of the first protective film byphotolithography process.

[0162] Lift-off method may also be employed to form the first protectivefilm 161 having such a stripe configuration as shown in FIG. 5A. Thatis, after forming a photoresist having slits formed in stripeconfiguration, the first protective film is formed over the entiresurface of the photoresist, and the photoresist is removed by dissolvingthereby leaving only the first protective film 161 which is in contactwith the contact layer 8. Well-shaped stripes having substantiallyvertical end faces can be obtained by the etching process describedabove rather than by forming the first protective film of stripeconfiguration by the lift-off method.

[0163] Then as shown in FIG. 5B, the first protective film 161 is usedas the mask for etching from the contact layer 8 the portion where thefirst protective film 161 is not formed, thereby to form the striperidge according to the shape of the protective film directly below thefirst protective film 161. When etching, structure and characteristic ofthe laser device vary depending on the position to stop etching.

[0164] As the means for etching the layer formed from nitridesemiconductor, dry etching is used such as RIE (reactive ion etching).For etching the first protective film made of Si oxide, it is preferableto use gas of fluorine compound such as CF₄. For etching the nitridesemiconductor in the second process, use of gas of chlorine compoundsuch as Cl₂, CCl₄ and SiCl₄ which are commonly used for the other GroupIII-V compound semiconductor makes the selectivity with respect to theSi oxide higher, and is therefore desirable.

[0165] Then as shown in FIG. 5C, a third protective film 163 is formedso as to cover a part of the stripe ridge. For the third protective film163, known resist film which has resistance to dry etching can be used,such as light-hardening resin. At this time, the stripe ridge covered bythe third protective film 163 becomes the second ridge 202 forconstituting the second waveguide region C₂, and the first ridge 201which constitutes the first waveguide region C₁ is formed in a regionnot covered by third protective film. The third protective film 163 andthe first protective film 161 formed as described above are used to etchthe laminate, where the masks are not formed, to such a depth as toreach the cladding layer, thereby to form the stripe ridges (firstridge) of different depths.

[0166] Then as shown in FIG. 7A, the second protective film 162 of aninsulating material different from that of the first protective film 161is formed on the side faces of the stripe ridge and on the surfaces ofthe layers which have been exposed by etching (cladding layers 5, 7 inFIG. 7). The first protective film 161 is made of a material differentfrom that of the second protective film 162, so that the firstprotective film 161 and the second protective film 162 are selectivelyetching. As a result, when only the first protective film 161 is removedby, for example, hydrofluoric acid, the second protective film 162 canbe formed continuously over the surfaces of the cladding layers 5, 7(the surfaces of the nitride semiconductor which have been exposed byetching) and the side faces of the ridge with the top surface of theridge being opened as shown in FIG. 7B. By forming the second protectivefilm 162 continuously as described above, high insulation property canbe maintained. In addition, when the second protective film 162 isformed continuously over the first protective film 161, the film can beformed with uniform thickness on the cladding layers 5, 7, and thereforecurrent concentration due to uneven film thickness does not occur. Sincethe etching is stopped amid the cladding layers 5, 7, the secondprotective film 162 is formed below the surfaces of the cladding layers5, 7 (top surfaces which are exposed). However, the second protectivefilm is formed on the layer where the etching was stopped when theetching is stopped below the cladding layers 5, 7, as a matter of fact.

[0167] In the next process, the first protective film 161 is removed bylift-off as shown in FIG. 7B. Then the electrode is formed on the secondprotective film 162 and the contact layer 8 so as to electricallycontact the contact layer 8. According to the present invention, sincethe second protective film having the striped openings is formed firston the ridge, it is not necessary to form the electrode only on thecontact layer of narrow stripe width, and it is made possible to formthe electrode of a large area which continues from the contact layerthat is exposed through the opening to the second insulation film. Thismakes it possible to form the electrode combining the electrode forohmic contact and the electrode for bonding together, by selecting theelectrode material that combines the function of ohmic contact.

[0168] When forming the stripe waveguide region in the nitridesemiconductor laser device, dry etching is employed because it isdifficult to etch by the wet process. Since selectivity between thefirst protective film and the nitride semiconductor is important in thedry etching process, SiO₂ is used for the first protective film.However, sufficient insulation cannot be achieved when SiO₂ is used alsoin the second protective film formed on the top surface of the layerwhere etching has been stopped, and the material is the same as that ofthe first protective film, it becomes difficult to remove the protectivefilm only. For this reason, a material other than SiO₂ is used for thesecond protective film thereby ensuring the selectivity with respect tothe first protective film in the present invention. Also because thenitride semiconductor is not etched after forming the second protectivefilm, difference in the etching rate between the second protective filmand the nitride semiconductor makes no problem.

[0169] (Method 2 for Forming the Stripe Ridge)

[0170]FIG. 16 is a schematic perspective view showing a part of a waferwhereon device structure is formed from nitride semiconductor, forexplaining the process of forming the semiconductor laser according tothe present invention. Processes of this method are substantiallysimilar to the processes of the method 1, although the end faces of theresonator are formed at the same time the n-type contact layer isexposed for forming the negative electrode by etching in the case ofthis method. Namely, the order of forming different portions isdifferent from the method 1. In the method 2, first the n-type contactlayer is exposed (FIG. 16A). At this time, the end faces of theresonator are formed at the same time. Then the stripe ridge, the firstand second waveguide regions and the electrode are formed similarly tothe method 1 (FIG. 16B). By forming the end faces of the resonator byetching first as described above, the invention can also be applied tosuch a case as good end faces of the resonator cannot be obtained bycleaving.

[0171] In the laser device of the present invention, as described above,the stripe ridge 202 for constituting the first waveguide region C₁ andthe second waveguide region C₂ can be efficiently formed, and theelectrode can be formed on the surface of the ridge of the laminate.

[0172] (Etching Means)

[0173] According to the manufacturing method of the present invention,when dry etching is used such as RIE (reactive ion etching) as the meansfor etching the layer formed from nitride semiconductor, it ispreferable to use gas of fluorine compound such as CF₄ for etching thefirst protective film made of Si oxide which is frequently used in thefirst process. For etching the nitride semiconductor in the secondprocess, use of gas of chlorine compound such as Cl₂, CCl₄ and SiCl₄which are commonly used for the other Group III-V compound semiconductormakes the selectivity with respect to the Si oxide higher, and istherefore desirable.

[0174] (Chip Formation)

[0175]FIG. 17 is a schematic sectional view showing the cutting positionwhen making chips out of the laminate formed on the wafer as describedpreviously. FIG. 17A shows only the substrate, and FIG. 17B shows a caseof dividing the substrate and the n-type layer. Regions each including apair of electrodes formed therein are dealt with as units and arereferred to as I, II, III and IV from left to right as shown in thedrawing. Ia, IIa and IVa in FIG. 17A are arranged so that the firstwaveguide region is directed to the right, and IIIa is directedopposite. Ib, IIb and IIIIb in FIG. 17B are arranged so that the firstwaveguide region is directed to the right, and IVb is directed opposite.Such an arrangement of the units before division may be selected asrequired.

[0176] When divided along line A-A, end faces of the resonator can beleft as formed by etching. In units I and II, an end face on the lightreflector side of the resonator is the cleaved facet when divided alongline B-B after being divided along line A-A. In II, the end face on thelight emitting side of the resonator is also the cleaved facet whendivided along line D-D. When divided along line C-C, end faces on thelight reflector side of the resonator in IIIa and IVa are formed ascleaved facets at the same time. Similarly, when divided along line E-E,end faces on the light emitting side of the resonator in IIIb and IVbare formed as cleaved facets at the same time. Thus the end face of thedevice and resonator end faces can be formed as etched surface orcleaved surface depending on the cut-off position.

[0177] In order to achieve such an arrangement as only the substrateexists between the resonator end face of Ia and the resonator end faceof IIb as between Ia and IIa shown in FIG. 17A, the work whereon theresonator end faces have been formed by etching as shown in FIG. 16B isfurther etched down to the substrate. The reason for etching down to thesubstrate is to prevent the semiconductor layer from cracking whendividing. In case the substrate is exposed in a single etching processby skipping the step shown in FIG. 16A, the surface near the activelayer which has been exposed by etching earlier becomes roughened due tolong duration of etching, thus making it difficult to obtain goodresonator end face. When the etching process is divided into two steps,first etching to the n-type layer as shown in FIG. 16A and then etchingdown to the substrate, good resonator end faces can be formed anddivision becomes easier. FIG. 16D shows the work shown in FIG. 16C beingcut off at the position indicated by the arrow. By applying etching intwo steps as described above, protrusion such as D in the drawing isformed. When etching down to the substrate, it is necessary to reducethe length of this protrusion D to the light emitting direction. This isbecause a large width D (length of protrusion) blocks the light emittedfrom the light emitting face and makes it difficult to obtain goodF.F.P. There will be no problem when D is small at least at the end faceon the light emitting side.

[0178] (Reflector Film)

[0179]FIG. 18 schematically shows the method of forming a reflector filmon the resonator end face. By disposing semiconductor which is dividedinto bar shape so that the end face on the light reflecting side or theend face on the light emitting side opposes the material of thereflector film, as shown in FIG. 18, the reflector film is formed bysputtering or the like. By forming the reflector film by sputteringwhile dividing the semiconductor into bar shape and disposing thecut-off face to oppose the material of the reflector film, high-qualityreflector film which has uniform thickness and is less likely todeteriorate can be formed even when the film is formed in multi-layeredstructure. Such a reflector film is more effective when used in a devicewhich is required to have a high output power and, particularly whenformed in multi-layered structure, the reflector film bearable to highoutput power can be made. The reflector film can be formed so as toextend to the resonator end face which is a side face even by sputteringfrom above the electrode. In this case, however, such an advantage asthe process to form into bar shape and directing the end face upward canbe eliminated, although uniform film cannot be obtained particularly inthe case of in multi-layered film since the film is formed from sidewaysonto the end face and therefore somewhat lower film quality results.Such a reflector film may be provided on both the light reflecting endface and the light emitting end face, or only on one end face anddifferent materials may be used.

[0180] According to the present invention, there is no limitation to theother device structure such as the active layer and the cladding layer,and various layer structures can be used. As a specific devicestructure, for example, the device structure shown in the embodiment tobe described later may be used. Also there is no limitation to theelectrode, and various constitutions of electrode can be used.Composition of the nitride semiconductors used in various layers of thelaser device is not restricted and nitride semiconductors represented bythe formula In_(b)Al_(c)Ga_(1−b−c)N (0≦b, 0≦d, b+d<1) can be used.

[0181] According to the present invention, any known methods of growingnitride semiconductor such as MOVPE, MOCVD (metalorganic chemical vaporphase deposition), HVPE (hallide vapor phase epitaxy) and MBE (molecularbeam epitaxy).

[0182] Embodiments

[0183] Now embodiment of the present invention will be described below.

[0184] While the following embodiments deal with laser devices made ofnitride semiconductor, the laser device of the present invention is notlimited to this constitution and the technology of the present inventioncan be applied to various semiconductors.

[0185] Embodiment 1

[0186] A laser device of the first embodiment will be described below.Specifically, the laser device comprising the second waveguide region C₂which has the sectional structure shown in FIG. 8 and the firstwaveguide region C₁ which has the sectional structure shown in FIG. 9 ismade as the first embodiment.

[0187] While a substrate made of sapphire, namely a material differentfrom the nitride semiconductor is used in the first embodiment, asubstrate made of nitride semiconductor such as GaN substrate may alsobe used. As the substrate of different material, an insulating substratesuch as sapphire and spinel (MgAl₂O₄) each having the principal plane ineither the C plane, R plane or A plane, SiC (including 6H, 4H and 3C),ZnS, ZnO, GaAs, Si, or an oxide which can be lattice-matched with thenitride semiconductor can be used as long as the nitride semiconductorcan be grown on the substrate. As the substrate of different material,sapphire and spinel are preferably used. The substrate of differentmaterial may have a plane inclined from the low index plane which iscommonly used (off-angle), in which case the base layer made of galliumnitride can be grown with good crystallinity by using a substrate whichhas stepwise off-angle configuration.

[0188] Also when the substrate of different material is used, aftergrowing the base layer made of the nitride semiconductor on thesubstrate, the substrate of different material is removed by polishingor other process to leave only the base layer before forming the devicestructure, and then the device structure may be formed by using the baselayer as the single substrate of the nitride semiconductor, or thesubstrate of different material may also be removed after forming thedevice structure.

[0189] In case the substrate of different material is used as shown inFIG. 8, device structure made of good nitride semiconductor can beformed by forming the device structure after forming the buffer layerand the base layer thereon. FIG. 8 is a sectional view showing thedevice structure in the second waveguide region C₂, and FIG. 9 is asectional view showing the device structure in the first waveguideregion C₁.

[0190] (Buffer Layer 102)

[0191] In the first embodiment, first, a substrate 101 of differentmaterial made of sapphire with the principal plane lying in the C planehaving diameter of 2 inches is set in a MOVPE reaction vessel,temperature is set to 500° C., and a buffer layer made of GaN is formedto a thickness of 200 Å by using trimethyl gallium (TMG) and ammonia(NH₃).

[0192] (Base Layer 103)

[0193] After growing the buffer layer 102, temperature is set to 1050°C. and a nitride semiconductor layer 103 made of undoped GaN is grown toa thickness of 4 μm by using TMG and ammonia. This layer is formed asthe base layer (substrate for film growth) for the constitution of thedevice. The base layer may also be formed from nitride semiconductor byELOG (Epitaxially Laterally Overgrowth), which makes it possible to growthe nitride semiconductor with good crystallinity. ELOG referscollectively to growing methods accompanied by lateral growth in which,for example, after growing a nitride semiconductor layer on a substrateof different material, the surface is covered by a protective film onwhich it is difficult to grow the nitride semiconductor formed thereonin the configuration of stripes at constant intervals, and nitridesemiconductor is grown newly from the nitride semiconductor surfaceexposed through the slits of the protective film, thereby covering theentire substrate with the nitride semiconductor. That is, when a maskedregion where a mask is formed and a non-masked region where the nitridesemiconductor is exposed are formed alternately and nitridesemiconductor is grown again from the surface of the nitridesemiconductor exposed through the non-masked region, the layer growsfirst in the direction of thickness but eventually grows also in thelateral direction as the growth proceeds so as to cover the maskedregion, thereby to cover the entire substrate.

[0194] The ELOG growth processes also include such a process as anopening is formed through which the substrate surface is exposed in thenitride semiconductor layer which has been grown first on the substrateof different material, and nitride semiconductor is grown from thenitride semiconductor located at the side face of the opening sideways,thereby forming the film.

[0195] According to the present invention, these various variations ofthe ELOG growth method can be employed. When nitride semiconductor isgrown by using the ELOG growth method, the nitride semiconductor formedby the lateral growth has good crystallinity and therefore a nitridesemiconductor layer having good overall crystallinity can be obtained.

[0196] Then the following layers which constitute the device structureare stacked on the base layer made of nitride semiconductor.

[0197] (n-type Contact Layer 104)

[0198] First, an n-type contact layer 3 made of GaN doped with Siconcentration of 1×10¹⁸/cm³ is formed to a thickness of 4.5 μm at atemperature of 1050° C. on the nitride semiconductor substrate (baselayer) 103 by using TMG, ammonia, and silane gas used as an impuritygas.

[0199] (Crack Preventing Layer 105)

[0200] Then a crack preventing layer 105 made of In_(0.06)Ga_(0,,94)N isformed to a thickness of 0.15 μm at a temperature of 800° C. by usingTMG, TMI (trimethyl indium), and ammonia. The crack preventing layer maybe omitted.

[0201] (n-type Cladding Layer 106)

[0202] After growing layer A made of undoped AlGaN to a thickness of 25Å is grown at a temperature of 1050° C. by using TMA (trimethylaluminum), TMG and ammonia as the stock material gas, supply of TMA isstopped and silane gas is used as the impurity gas, and layer B made ofGaN doped with Si concentration of 5×10¹⁸/cm³ is formed to a thicknessof 25 Å. This operation is repeated 160 times to stack the layer A andlayer B to form the n-type cladding layer 106 made in multi-layered film(super lattice structure) having a total thickness of 8000 Å. At thistime, a difference in the refractive index sufficient for the claddinglayer to function can be provided when the proportion of Al of theundoped AlGaN is in a range from 0.05 to 0.3.

[0203] (n-type Optical Guide Layer 107)

[0204] Then at a similar temperature, an n-type optical guide layer 107made of undoped GaN is formed to a thickness of 0.1 μm by using TMG andammonia as the stock material gas. The n-type optical guide layer 107may be doped with an n-type impurity.

[0205] (Active Layer 108)

[0206] Then by setting the temperature to 800° C., a barrier layer madeof In_(0.05)Ga_(0,,95)N doped with Si in a concentration of 5×10¹⁸/cm³to a thickness of 100 Å by using TMI (trimethyl indium), TMG and ammoniaas the stock material gas and silane gas as the impurity gas. Then thesupply of silane gas is stopped and a well layer made of undopedIn_(0.1)Ga_(0,,9)N is formed to a thickness of 50 Å. This operation isrepeated three times thereby to form the active layer 108 of multiplequantum well structure (MQW) having total thickness of 550 Å with thelast layer being the barrier layer.

[0207] (p-type Electron Confinement Layer 109)

[0208] Then at a similar temperature, a p-type electron confinementlayer 109 made of AlGaN doped with Mg in a concentration of 1×10¹⁹/cm³is formed to a thickness of 100 Å by using TMA, TMG and ammonia as thestock material gas and Cp₂Mg (cyclopentadienyl magnesium) as theimpurity gas. This layer may not be provided, though would function aselectron confinement layer and help decrease the threshold whenprovided.

[0209] (p-type Optical Guide Layer 110)

[0210] Then by setting the temperature to 1050° C., a p-type opticalguide layer 110 made of undoped GaN is formed to a thickness of 750 Å byusing TMG and ammonia as the stock material gas.

[0211] While the p-type optical guide layer 110 is grown as an undopedlayer, diffusion of Mg from the p-type electron confinement layer 109increases the Mg concentration to 5×10¹⁶/cm³ and turns the layer p-type.Alternatively, this layer may be intentionally doped with Mg whilegrowing.

[0212] (p-type Cladding Layer 111)

[0213] Then a layer of undoped Al_(0.16)Ga_(0.84)N is formed to athickness of 25 Å at 1050° C., then supply of TMA is stopped and a layerof Mg-doped GaN is formed to a thickness of 25 Å by using Cp₂Mg. Thisoperation is repeated to form the p-type cladding layer 111 constitutedfrom super lattice structure of total thickness of 0.6 μm. When thep-type cladding layer is formed in super lattice structure consisting ofnitride semiconductor layers of different band gap energy with at leastone thereof including Al being stacked one on another, crystallinitytends to be improved by doping one of the layers more heavily than theother, in the so-called modulated doping. In the present invention,however, both layers may be doped similarly. The cladding layer is madein super lattice structure consisting of nitride semiconductor layerswhich include Al, preferably Al_(x)Ga_(1−x)N (0<X<1), more preferablysuper lattice structure consisting of GaN and AlGaN stacked one onanother. Since the p-type cladding layer 111 formed in the super latticestructure increases the proportion of Al in the entire cladding layer,refractive index of the cladding layer can be decreased. Also becausethe band gap energy can be increased, it is very effective in reducingthe threshold. Moreover, since pits generated in the cladding layer canbe reduced by the super lattice structure compared to a case withoutsuper lattice structure, occurrence of short-circuiting is also reduced.

[0214] (p-type Contact Layer 112)

[0215] Last, at a temperature of 1050° C., a p-type contact layer 112made of p-type GaN doped with Mg in a concentration of 1×10²⁰/cm³ isformed to a thickness of 150 Å on the p-type cladding layer 111. Thep-type contact layer may be formed from p-type In_(x)Al_(y)Ga_(1−x−y)N(0≦X, 0≦Y, X+Y≦1), and preferably from Mg-doped GaN which achieves thebest ohmic contact with the p-type electrode 20. Since the contact layer112 is the layer where the electrode is to be formed, it is desirable tohave a high carrier concentration of 1×10¹⁷/cm³ or higher. When theconcentration is lower than 1×10¹⁷/cm³, it becomes difficult to achievesatisfactory ohmic contact with the electrode. Forming the contact layerin a composition of GaN makes it easier to achieve satisfactory ohmiccontact with the electrode. After the reaction has finished, the waferis annealed in nitrogen atmosphere at 700° C. in the reaction vesselthereby to further decrease the electrical resistance of the p-typelayer.

[0216] After forming the nitride semiconductor layers one on another asdescribed above, the wafer is taken out of the reaction vessel. Then aprotective film of SiO₂ is formed on the surface of the top-most p-typecontact layer, and the surface of the n-type contact layer 104 whereonthe n-type electrode is to be formed is exposed as shown in FIG. 8 byetching with SiCl₄ gas in the RIE (reactive ion etching) process. Forthe purpose of deep etching of the nitride semiconductor, SiO₂ is bestsuited as the protective film. At the same time the n-type contact layer104 is exposed, end faces of the active layer which would become theresonance end face may also be exposed thereby making the etched endface serve as the resonance end face.

[0217] Now a method for forming the first waveguide region C₁ and thesecond waveguide region C₂ as the stripe waveguide region will bedescribed in detail below. First, a first protective film havingthickness of 0.5 μm is formed from Si oxide (mainly SiO₂) oversubstantially the entire surface of the top-most p-type contact layer(upper contact layer) 8 by means of a PDP apparatus. Then the firstprotective film 161 is formed by patterning (refer to FIG. 5A used inthe description of the embodiment). Patterning of the first protectivefilm 161 is carried out by means of photolithography process and the RIE(reactive ion etching) apparatus which employs SiF₄ gas. Then by usingthe first protective film 161 as the mask, a part of the p-type contactlayer 112 and the p-type cladding layer 111 is removed so that thep-type cladding layer 111 remains with a small thickness on both sidesof the mask, thereby forming striped ridges over the active layer 3(refer to FIG. 5B used in the description of the embodiment). Thisresults in the second ridge 202 which constitutes the second waveguideregion C₂ being formed. At this time, the second ridge is formed byetching a part of the p-type contact layer 112 and the p-type claddinglayer 111, so that the p-type cladding layer 111 is etched to a depth of0.01 μm.

[0218] After forming the striped second ridge, a photoresist film isformed as the third protective film 163 except for a part of the secondridge (the portion which constitutes the first waveguide region) (referto FIG. 5C used in the description of the embodiment). The firstprotective film 161 remains on the top surface of the ridge in theportion where the second waveguide region is to be formed and on the topsurface of the ridge in the portion where the first waveguide region isto be formed.

[0219] Then after transferring to the RIE (reactive ion etching)apparatus, the third protective film 163 and the first protective film161 are used as the masks to etch on both sides of the first protectivefilm 161 in the portion where the first waveguide region is to be formedto such a depth as the n-type cladding layer 106 is exposed by usingSiF₄ gas, thereby to form the first ridge of stripe configuration whichconstitutes the first waveguide region C₁. At this time, the first ridgeformed in the stripe configuration is formed by etching the n-typecladding layer 106 on both sides of the first ridge to such a depth asthe thickness becomes 0.2 μm.

[0220] The wafer having the first waveguide region C₁ and the secondwaveguide region C₂ formed thereon is then transferred to the PVDapparatus, where the second protective film 162 made of Zr oxide (mainlyZrO₂) with a thickness of 0.5 μm continuously on the surface of thefirst protective film 161, on the side faces of the first and secondridges, on the p-type cladding layer 111 which is exposed by etching andon the n-type cladding layer 106 (refer to FIG. 7A used in thedescription of the embodiment).

[0221] After forming the second protective film 162, the wafer issubjected to heat treatment at 600° C. When the second protective filmis formed from a material other than SiO₂, it is preferable to applyheat treatment at a temperature not lower than 300° C., preferably 400°C. or higher but below the decomposition temperature of the nitridesemiconductor (1200° C.) after forming the second protective film, whichmakes the second protective film less soluble to the material(hydrofluoric acid) which dissolves the first protective film.

[0222] Then the wafer is dipped in hydrofluoric acid to remove the firstprotective film 161 (lift-off process). Thus the first protective film161 provided on the p-type contact layer 112 is removed thereby exposingthe p-type contact layer 112. The second protective film 162 is formedon the side faces of the first ridge 201 and the second ridge 202 whichare formed in stripes on the first waveguide region C₁ and the secondwaveguide region C₂, and on the surface located on both sides of theridge continuing thereto (the surface of the p-type cladding layer 111located on both side of the second ridge and the surface of the n-typecladding layer located on both side of the first ridge) by the processdescribed above (refer to FIG. 7C used in the description of theembodiment).

[0223] After the first protective film 161 provided on the p-typecontact layer 112 is removed as described above, a p-type electrode 120made of Ni/Au is formed on the surface of the exposed p-type contactlayer making ohmic contact therewith. The p-type electrode 120 is formedwith stripe width of 100 μm over the second protective film 162 as shownin FIG. 8. At this time, the p-type electrode 120 is formed only in thefirst waveguide region C₁ and the second waveguide region C₂ in thedirection of stripe in the first embodiment. In the first embodiment,the p-type electrode 120 is formed to such a length that does not reachboth ends of the second waveguide region C₂. After forming the secondprotective film 162, an n-type electrode 21 made of Ti/Al is formed in adirection parallel to the stripe on the n-type contact layer 104 whichhas been already exposed.

[0224] Then the region where lead-out electrodes for the p-type andn-type electrodes are to be formed is masked, and a multi-layereddielectric film 164 made of SO₂ and TiO₂ are formed. With the mask beingremoved, apertures for exposing the p-type and n-type electrodes areformed in the multi-layered dielectric film 164. Through the apertures,the lead-out electrodes 122, 123 made of Ni—Ti—Au (1000 Å-1000 Å-8000 Å)are formed on the p-type and n-type electrodes. In the first embodiment,the active layer 108 in the second waveguide region C₂ is formed with awidth of 200 μm (width in the direction perpendicular to the resonatordirection) The guide layer is also formed with a similar width.

[0225] After forming the p-type and n-type electrodes, the resonance endfaces are formed on the ends of the first waveguide region C₁ and thesecond waveguide region C₂ by etching further till the substrate isexposed.

[0226] In the laser device of the first embodiment, the resonator wasformed with total length of 650 μm and the first waveguide region C₁ wasformed with total length of 5 μm including one of the end faces of theresonator. Thus the second waveguide region C₂ has total length of 645μm including the other end face. On the end faces of the resonator whichare formed by etching, the multi-layered dielectric film made of SiO₂and TiO₂ was formed. Then sapphire substrate of the wafer is polished toa thickness of 70 μm and is divided from the substrate side into barshape with the wafer of bar shape further divided into individualdevices, thereby to obtain the laser devices.

[0227] While the resonance end face is formed by forming themulti-layered dielectric film on the etched surface in the firstembodiment, the wafer may be divided into bar shape along (11-00) Msurface which is cleaved surface of GaN to use the surface as theresonance end face.

[0228] With the laser device of the first embodiment fabricated asdescribed above, continuous oscillation at wavelength 405 nm with anoutput power of 30 mW was confirmed with threshold of 2.0 kA/cm² at roomtemperature. Also good beam of F.F.P. was obtained with aspect ratio of1.5, indicating satisfactory beam characteristics for the light sourceof an optical disk system. The excellent characteristics are achievedthrough such features of the present invention that laser beam ofdesired optical characteristics can be emitted by adjusting the width ofthe ridge of the first waveguide region C₁ on the light emitting sideregardless of the stripe width of the second waveguide region C₂ whichfunctions mainly as a gain region. Also the laser device of the firstembodiment does not experience a shift in the transverse mode in theoptical output range from 5 to 30 mW, and therefore has favorablecharacteristic suitable for reading and writing light source of anoptical disk system. In addition, the laser device having goodperformance when driven with 30 mW comparable to the conventionalrefractive-index guided laser device.

[0229] Also in the first embodiment, the p-type electrode may beprovided over a length that covers the first waveguide region C₁ asshown in FIG. 7C. With this constitution, too, the laser device havingexcellent beam characteristics and long service life can be made.

[0230] [Embodiment 2]

[0231] The laser device is fabricated similarly to the first embodimentexcept for the length of the first waveguide region C₁ which is set to 1μm. In order to form the first waveguide region C₁ with such a smalllength, the first ridge of stripe shape is formed longer than the finallength of the resonator (for example, several tens to about 100 μm) andthen the resonance end face is formed by etching or dividing thesubstrate at such a position as the desired length of the firstwaveguide region C₁ is obtained. As a result, it becomes more difficultto form the second ridge 201 with stable shape than in the case of thefirst embodiment, although the transverse oscillation mode can be wellcontrolled even with this length. Also shorter length of the firstwaveguide region improves the device life slightly over the firstembodiment.

[0232] [Embodiment 3]

[0233] The laser device of the third embodiment is constituted similarlyto the first embodiment except for forming the first waveguide regionsC₁ having length of 5 μm at both ends thereof (refer to FIG. 4B). Thatis, the laser device of the third embodiment has the second waveguideregion C₂ located at the center and the first waveguide regions C₁located on both sides of the former, while the first waveguide region C₁includes the resonator end face. The laser device of the thirdembodiment having such a constitution has both F.F.P. and aspect rationof the beam similar to those of the first embodiment.

[0234] [Embodiment 4]

[0235] The laser device is constituted similarly to the first embodimentexcept that the second ridge 202 provided to constitute the secondwaveguide region C₂ is formed by etching to leave the p-type guide layerhaving a thickness of 500 Å on both sides of the second ridge. Whilelaser device thus obtained has lower threshold than that of the firstembodiment, beam characteristics similar to those of the firstembodiment are obtained.

[0236] [Embodiment 5]

[0237] The laser device of the fifth embodiment is constituted similarlyto the first embodiment except for providing a slant surface between thefirst waveguide region C₁ and the second waveguide region C₂ (refer toFIG. 4A) Specifically, in the fifth embodiment, in the boundary betweenthe first waveguide region C₁ and the second waveguide region C₂, thesectional surfaces formed by etching between the surface of the n-typecladding layer 106 located on both sides of the first ridge and thesurface of the p-type cladding layer 111 located on both sides of thesecond ridge is inclined to 90° with respect to the surface of then-type cladding layer 106.

[0238] Though the laser device manufactured as described above may besubjected to variations in the device characteristics compared to thefirst embodiment, the effect of the present invention that goof F.F.P.is obtained and the reliability is improved can be achieved.

[0239] [Embodiment 6]

[0240] The laser device of the sixth embodiment is constituted similarlyto the first embodiment except for providing the third waveguide regionC₃ between the first waveguide region C₁ and the second waveguide regionC₂ as shown in FIG. 13. Specifically, in the laser device of the sixthembodiment, after the second ridge 202 to a depth reaching the layer ofsecond conductivity type (p-type cladding layer 111), the thirdwaveguide region C₃ having a side face 204 formed to have an angle α of20° from the resonator direction AA is formed at the same time when thefirst ridge is formed by etching down to the layer of first conductivitytype (n-type cladding layer 106). Thus the laser device of the sixthembodiment which has the third waveguide region C₃ in addition to thefirst waveguide region C₁ and the second waveguide region C₂ is made. Inthe laser device of the sixth embodiment constituted as described above,light which has been guided while spreading in the active layer plane inthe second waveguide region C₂ is reflected on the side face 204 of thethird waveguide region C₃ and is directed toward the first waveguideregion C₁, and therefore the light can be guided smoothly. That is, asthe light guided in the direction of the resonator falls on the sideface 204 with an incident angle of (90°−α), the light undergoes totalreflection on the side face 204 and can be guided into the stripewaveguide region without loss. In the second waveguide region C₂ and thethird waveguide region C₃, effective difference in the refractive indexis provided in the active layer plane by means of the second ridge 202which is provided on the layer of second conductivity type (p-typecladding layer 111), and the stripe waveguide region is formed. In thethird waveguide region C₃, light guided while coming out of the regionright below the second ridge can be guided satisfactorily into the firstwaveguide region C₁.

[0241] In the sixth embodiment, as described above, since the side face204 is inclined against the side face of the first ridge 201 in thefirst waveguide region C₁, light can be smoothly guided. The boundarybetween the side face 204 and the second waveguide region C₂ may also beconnected directly to the second waveguide region C₂ without bending asshown in FIG. 13.

[0242] In the laser device of the sixth embodiment, as described above,since light guided in the stripe waveguide region in the active layerplane or coming out thereof in the second waveguide region C₂ can beefficiently guided into the first waveguide region C₁, the devicecharacteristics can be improved. In the laser device of the sixthembodiment, in particular, threshold of current density can be decreasedand slope efficiency can be improved.

[0243] [Embodiment 7]

[0244] The laser device of the seventh embodiment is constitutedsimilarly to the first embodiment except for constituting the firstwaveguide region C₁ in 2-step configuration where the side face isformed in two steps.

[0245] Specifically, in the seventh embodiment, after forming thestriped ridge by etching to such a depth that does not reach the activelayer, a ridge wider than the stripe width of the ridge is etched downto the n-type cladding layer 106 in a portion where the first waveguideregion is to be formed, thereby to form the 2-step ridge.

[0246]FIG. 14A is a perspective view showing the laser device structureof the seventh embodiment, FIG. 14C is a sectional view of the firstwaveguide region C₁ and FIG. 14B is a sectional view of the secondwaveguide region C₂. In the laser device of the seventh embodiment, asshown in FIG. 14A, the first waveguide region C₁ is formed in the formof 2-step ridge comprising an upper ridge of width S_(w1) and a lowerridge of width S_(w2). In the first waveguide region C₁, since theactive layer is located in the lower ridge, and width of the activelayer 3 is determined by the width S_(w2) of the lower ridge, thewaveguide can be considered to be formed substantially by the lowerridge. The structure of the seventh embodiment makes it easier tocontrol the width S_(w2) of the lower ridge compared to a case where thefirst ridge is formed as in the first embodiment or the like and, as aresult, width of the active layer of the first waveguide region can beformed accurately. This is because, while etching is carried out in twosteps with a single mask when the first ridge 201 for constituting thefirst waveguide region C₁ is formed by the method shown in FIG. 5, astep is formed in the boundary between the portion shared by the secondridge which has been formed first and the portion below thereof duringthe second etching to such a depth that reaches the layer of firstconductivity type, thus making it unreliable to accurately control thewidth of the lower portion.

[0247] According to the seventh embodiment, in contrast, after etchingthe upper ridge in the etching process common to the second ridge, thelower ridge is formed through etching by making and using a maskdifferent from the mask used when forming the upper ridge. Consequently,the lower ridge can be formed with accurate width while the active layer3 located in the lower ridge can also be formed with accurate width.

[0248] Thus according to this embodiment, laser device havingcharacteristics equivalent to the first embodiment can be manufacturedwith less variations due to manufacturing. In other words, the laserdevice of the seventh embodiment is advantageous with respect tomanufacturing.

[0249] [Embodiment 8]

[0250] The laser device structure of the eighth embodiment has the thirdwaveguide region formed between the first waveguide region and thesecond waveguide region, with the third waveguide region beingconstituted differently from the sixth embodiment.

[0251] Specifically, in the laser device structure of the eighthembodiment, the third waveguide region C₃ is constituted from a thirdridge provided on the p-type cladding layer 111 and the p-type contactlayer 112 as shown in FIG. 15A, with the third ridge decreasing in widthtoward the first waveguide region.

[0252] Thus according to the eighth embodiment, forming the thirdwaveguide region makes it possible to connect the first waveguide regionand the second waveguide region, which have different widths, withoutchanging the width of the waveguide discretely.

[0253]FIG. 15A is a perspective view showing the laser device structureof the eighth embodiment, and FIG. 15B is a cross sectional view of theactive layer. In FIG. 15B, width S_(w1) is the width of the second ridgeat the base thereof, and width S_(w2) is the width of the active layerportion of the first ridge.

[0254] The imaginary line (a dash and two dots line) in FIG. 15B is theprojection of the second ridge and the third ridge onto the crosssectional plane of the active layer. Since the waveguides of the secondwaveguide region and the third waveguide region are constituted byproviding the effective difference in the refractive index in the activelayer corresponding to the second ridge and the third ridge, theimaginary line (a dash and two dots line) can be considered tosubstantially represent the waveguides of the second waveguide regionand the third waveguide region.

[0255] The laser device structure of the eighth embodiment manufacturedas described above shows excellent characteristics similarly to that ofthe first embodiment.

[0256] [Embodiment 9]

[0257] The ninth embodiment is an example of manufacturing the laserdevice which is constituted similarly to the first embodiment by amethod different from the first embodiment.

[0258] In the ninth embodiment, the second ridge is formed after thefirst ridge has been formed.

[0259] Specifically, after forming the layers one on another similarlyto the first embodiment, the first protective film 161 having stripeshape is formed on the surface of the laminate as shown in FIG. 5A. Thenas shown in FIG. 6A, the third protective film 163 is formed except fora part of the first protective film 161 (where the first waveguideregion is to be formed), and both sides of the first protective film 161are etched to such a depth as the lower cladding layer 5 (n-typecladding layer 106) is exposed, thereby to form the first ridge 201 asshown in FIG. 6B. Then after temporarily removing the third protectivefilm 163, the third protective film 163 is formed to cover the firstridge 201 as shown in FIG. 6C. Under this condition, portions where thesecond waveguide region is to be formed except for those on both sidesof the first protective film 161 are covered by at least one of thefirst protective film and the third protective film 163. After creatingthis state, the second ridge is formed by etching the regions which arenot covered by the first protective film 161 and the third protectivefilm 163 to such a depth that does not reach the active layer.

[0260] At this time, width and height of ridges that constitute thefirst waveguide region C₁ and the second waveguide region C₂ are set tosimilar values as the first embodiment. Then the third protective film163 provided on the first waveguide region C₁ is removed to leave onlythe first protective film 161 which is the striped mask, followed by asubsequent process similar to the first embodiment wherein the secondprotective film (buried layer) is formed on the side face of the stripeand on the surface of the nitride semiconductor layer which continuestherefrom. Then the laser device is obtained similarly to the firstembodiment. According to the method of the ninth embodiment describedabove, although the number of processes increases compared to the methodof the first embodiment, laser device similar to that of the firstembodiment can be manufactured.

[0261] [Embodiment 10]

[0262] The tenth embodiment is an example of manufacturing the laserdevice by using a nitride semiconductor substrate, with the basic deviceconstitution having the second waveguide region C₂ of the structureshown in FIG. 8 and the first waveguide region C₁ of the structure shownin FIG. 9.

[0263] (Substrate 101)

[0264] In the tenth embodiment, the nitride semiconductor substrate madeof GaN 80 μm thick which is fabricated as follows is used.

[0265] As the substrate of different material where on the nitridesemiconductor is to be grown, a sapphire substrate measuring 425 μm inthickness and 2 inches in diameter with the principal plane lying on theC plane and orientation flat surface on the A plane is prepared. Thewafer is set in a MOCVD reaction vessel. Then with the temperature setto 510° C. and using hydrogen as the carrier gas and ammonia and TMG(trimethyl gallium) as the stock material gas, a low-temperature growthbuffer layer made of GaN is formed to a thickness of 200 Å on thesapphire substrate, followed by the growth of a base layer made ofundoped GaN is grown to a thickness of 2.5 μm by using TMG and ammoniaas the stock material gas, with the temperature set to 1050° C. Aplurality of masks made of SiO₂ and in the shape of stripe each 6 μmwide are formed in parallel to each other, in a direction of θ=0.3° fromthe direction perpendicular to the orientation flat surface (A plane) ofthe sapphire substrate, so that the interval between masks (aperture ofthe mask) is 14 μm. Then the substrate is returned to the MOCVDapparatus where the undoped GaN is grown to a thickness of 15 μm. Inthis process, GaN which is grown selectively through the mask aperturegrows mainly in the longitudinal direction (thickness direction) in themask aperture, and grows in the lateral direction over the mask, so thatthe base layer covering the mask and the mask aperture is formed. In thebase layer which has grown as described above, occurrence of throughdislocation in the nitride semiconductor layer that has grown laterallycan be decreased. Specifically, through dislocation occurs in such a wayas the dislocation density increases to about 10¹⁰/cm² over the maskaperture and around the center of the mask where fronts of growingnitride semiconductor bodies approaching laterally from both sides ofthe mask join, and the dislocation density decreases to about 10⁸/cm²over the mask except for the central portion thereof.

[0266] Then the wafer is placed in the HVPE apparatus where undoped GaNis grown to a thickness of about 100 μm on the base layer (the layergrown to about 100 μm thick will be referred to as thick film layer).Then the substrate of different material, the low-temperature growthbuffer layer, the base layer and a part of the thick film layer areremoved thereby to leave only the thick film layer (singularization) andobtain a GaN substrate 80 μm thick. Although the thick film layer formedby the HVPE may be made of a nitride semiconductor other than GaN, it ispreferable to use GaN or AlN which makes it possible to easily growthick nitride semiconductor layer with good crystallinity, according tothe present invention. The substrate of different material may beremoved either after forming the device structure which will bedescribed later, or after forming the waveguide, or after forming theelectrode. When the substrate of different material is removed beforecutting the wafer into bars or chips, cleavage planes of the nitridesemiconductor ({11-00} M plane, {1010} A plane, {0001} C planeapproximated by hexagonal system) can be used when cutting or cleavinginto chips.

[0267] (Base Layer 102)

[0268] A base layer 102 is formed to a thickness of about 15 μm on thenitride semiconductor substrate so as to grow in the lateral directionas well. By using a striped SiO₂ mask similarly to the base layer usedwhen fabricating the nitride semiconductor substrate.

[0269] [Buffer Layer 103]

[0270] A buffer layer 103 made of undoped AlGaN with Al proportion of0.01 is formed on the base layer 102. Although the buffer layer 103 maybe omitted, in case the substrate which uses lateral growth is made ofGaN, or in case the base layer formed by using lateral growth is made ofGaN, it is preferable to form the buffer layer 103 since the occurrenceof pits can be decreased by using the buffer layer 103 made of a nitridesemiconductor which has lower thermal expansion coefficient than tat ofGaN, namely A_(a)Ga_(1−a)N (0<a≦1) or such material. That is, pits arelikely to occur when a nitride semiconductor is grown on other type ofnitride semiconductor which has been grown in a process accompanied bylateral growth as in the case of the base layer 102, while the bufferlayer 103 has an effect of preventing the occurrence of pits.

[0271] It is also preferable that the proportion a of Al contained inthe buffer layer 103 is 0<a<0.3, which makes it possible to form abuffer layer of good crystallinity. After forming the buffer layer 103,an n-type contact layer of composition similar to that of the bufferlayer may be formed, thereby giving the buffer effect also to the n-typecontact layer 104. That is, the buffer layer 103 decreases the pits andimproves the device characteristics when at least one layer thereof isprovided between the laterally-grown layer (GaN substrate) and thenitride semiconductor layer which constitutes the device structure, orbetween the active layer within the device structure and thelaterally-grown layer (GaN substrate), and more preferably on thesubstrate side in the device structure, between the lower cladding layerand the laterally-grown layer (GaN substrate). When a buffer layer whichalso performs the function of the n-type contact layer, proportion a ofAl contained therein is preferably within 0.1 so as to obtain good ohmiccontact with the electrode. The buffer layer formed on the base layer102 may be grown at a low temperature in a range from 300 to 900° C.similarly to the buffer layer which is provided on the substrate ofdifferent material described above, the effect of reducing the pits canbe improved by single crystal growth at a temperature in a range from800 to 1200° C. Moreover, the buffer layer 103 may be either doped withn-type or p-type impurity or undoped, although it is preferable to growwithout doping in order to obtain good crystallinity. In case two ormore layers of buffer layer are provided, the layer can be formed whilechanging the concentration of n-type or p-type impurity and/or theproportion of Al.

[0272] (n-type Contact Layer 104)

[0273] The n-type contact layer 104 made of Al_(0.01)Ga_(0,,99)N dopedwith Si in a concentration of 3×10¹⁸/cm³ is formed to a thickness of 4μm on the buffer layer 103.

[0274] (Crack Preventing Layer 105)

[0275] A crack preventing layer 105 made of In_(0.06)Ga_(0,,94)N isformed to a thickness of 0.15 μm on the n-type contact layer. 104.

[0276] (n-type Cladding Layer 106)

[0277] An n-type cladding layer 106 of super lattice structure to totalthickness of 1.2 μm on the crack preventing layer 105.

[0278] Specifically, the n-type cladding layer 106 is formed by formingundoped In_(0.05)Ga_(0,,95)N to a thickness of 25 μm and GaN layer dopedwith Si in a concentration of 1×¹⁹/cm³ alternately one on another.

[0279] (n-type Optical Guide Layer 107)

[0280] An n-type optical guide layer 107 made of undoped GaN of athickness of 0.15 μm is formed on the n-type cladding layer 106.

[0281] (Active Layer 108)

[0282] The active layer 108 of multiple quantum well structure withtotal thickness of 550 Å on the n-type optical guide layer 107.

[0283] Specifically, the active layer 108 is formed by forming thebarrier layer (B) made of In_(0.05)Ga_(0,,95)N doped with Si in aconcentration of 5×10¹⁸/cm³ with a thickness of 140 Å and a well layer(W) made of undoped In_(0.13)Ga_(0,,87)N with a thickness of 50 Åalternately in the order of (B)-(W)-(B)-(W)-(B).

[0284] (p-type Electron Confinement Layer 109)

[0285] The p-type electron confinement layer 109 made of p-typeAl_(0.3)Ga_(0,,7)N doped with Mg in a concentration of 1×10²⁰/cm³ isformed to a thickness of 100 Å on the active layer 108.

[0286] (p-type Optical Guide Layer 110)

[0287] The p-type optical guide layer 110 made of p-type GaN doped withMg in a concentration of 1×10¹⁸/cm³ is formed to a thickness of 0.15 μmon the p-type electron confinement layer 109.

[0288] (p-type Cladding Layer 111)

[0289] A p-type cladding layer 111 of super lattice structure with totalthickness of 0.45 μm is formed on the optical guide layer 110.

[0290] Specifically, the p-type cladding layer 111 is formed by formingundoped Al_(0.05)Ga_(0,,95)N of thickness 25 Å and p-type GaN layerdoped with Mg in a concentration of 1×10²⁰/cm³ of thickness 25 Åalternately one on another.

[0291] (p-type Contact Layer 112)

[0292] The p-type contact layer 112 made of p-type GaN doped with Mg ina concentration of 2×10²⁰/cm³ is formed to a thickness of 150 Å on thep-type cladding layer 111.

[0293] After forming the device structure from the n-type contact layer104 to the p-type contact layer 112 as described above, the n-typecontact layer 104 is exposed, the 31 and the second waveguide region C₂are formed by etching, and the second protective film 162 (buried layer)is formed on the side faces of the first ridge and the second ridge andon the nitride semiconductor layer surface which continues thereto,similarly to the first embodiment. At this time, the second ridgeprovided for constituting the second waveguide region C₂ is formed byetching the p-type optical guide layer 110 on both sides of the secondridge to such a depth as the film thickness becomes 0.1 μm.

[0294] Now the method for forming the resonating end face of the laserdevice according to the tenth embodiment will be described below.

[0295] In the tenth embodiment, the resonating end faces are formedefficiently by disposing a pair of laser devices so that the two devicesoppose each other in a symmetrical arrangement with respect to a planeof symmetry.

[0296] Specifically, the second waveguide regions C₂ each 645 μm inlength are formed on both sides of the first waveguide region C₁ whichis 10 μm long (the first waveguide regions of a pair of laser devicescoupled) (refer to FIG. 17B at portions IIIb and IVb).

[0297] The outer end faces of the second waveguide regions C₂ on bothsides thereof are formed at the same time as the etching for exposingthe n-type contact layer.

[0298] Then similarly to the first embodiment, the n-type electrode 121and the p-type electrode 120 are formed on the surfaces of the n-typecontact layer 104 and the p-type contact layer 112.

[0299] Then an insulation film (reflector film) 164 made of a dielectricmulti-layered film is formed over the entire surfaces which are exposedincluding the end faces of the second waveguide region and the sidefaces of each ridge provided for constituting the waveguide regions.

[0300] This process forms the insulation film 164 which functions as areflector film at the end face of the second waveguide region C₂ andfunctions as an insulation film in other parts (particularly functionsto prevent short-circuiting between p-n electrodes). In the tenthembodiment, the p-type electrode 120 is formed on a part of the p-typecontact layer 112 with a width smaller than the stripe width of thep-type contact layer 112., unlike those shown in FIGS. 8 and 9. Thep-type electrode 120 is formed only on the top of the second waveguideregion C₂ in the direction of stripe. The p-type electrode 120 is formedat a small distance from the end of the second waveguide region C₂.

[0301] Then a part of the insulation film 164 provided on the n-type andp-type electrodes is removed to expose the electrodes, thereby to formpad electrodes 122, 123 which make electrical connection on the surfacesof the electrodes.

[0302] Then at around the center of the first waveguide region C₁ whichis 10 μm (refer to line E-E in FIG. 17B), the nitride semiconductor iscleaved along M surface into bar shape, and the bars are cleaved inparallel to the resonator direction along A plane perpendicular to the Mplane of cleaving between the devices, thereby to obtain chips.

[0303] The laser chip obtained as described above has the firstwaveguide region C₁ having length of about 5 μm and the second waveguideregion C₂ having length of 645 μm, with the end face of the firstwaveguide region C₁ being used as the light emitting side, similarly tothe first embodiment.

[0304] The laser device obtained as described above has thresholdcurrent density of 2.5 kA/cm² and threshold voltage of 4.5V at roomtemperature, with oscillation wavelength of 405 nm and aspect ratio of1.5 for the laser beam emitted. With continuous oscillation at 30 mW,the laser device can operate with a high output power for 1000 hours orlonger. The laser device is capable of continuous oscillation in anoutput range from 5 mW to 80 mW, and has beam characteristics suited asthe light source for optical disk systems in this output range.

[0305] [Embodiment 11]

[0306] The laser device of the eleventh embodiment is constituted byusing Si-doped n-type GaN which is 80 μm thick as the substrate 101instead of the undoped GaN which is 80 μm thick of the tenth embodiment,The substrate 101 made of Si-doped n-type GaN is made by forming a lowtemperature growth buffer layer on a substrate of different material,forming a base layer in a growing process which is accompanied bylateral growth, forming a thick film of Si-doped n-type GaN to athickness of 100 μm by HVPE, and then removing the substrate ofdifferent material.

[0307] In the eleventh embodiment, the buffer layer 103 made of Si-dopedAl_(0.01)Ga_(0,,99)N is formed on the n-type GaN substrate 101, andthereon the layers are formed one on another from the n-type contactlayer 104 to the p-type contact layer 112 similarly to the firstembodiment.

[0308] Then a separation groove is formed by etching so as to expose thesurface of the p-type contact layer 112 in order to define the regionwhere the waveguide regions of the deices are to be formed. In theeleventh embodiment, unlike the first embodiment, it is not necessary toprovide a space for forming the n-type electrode on the exposed surfaceof the n-type contact layer in order to make a structure of opposingstructure of electrodes on both sides of the substrate without forming apair of positive and negative electrodes on the same side. Therefore,adjacent devices can be disposed nearer to each other than in the caseof the tenth embodiment.

[0309] In the eleventh embodiment, different regions are defined byexposing the n-type contact layer by etching, but the following processmay also be carried out without etching for achieving opposingarrangement in this constitution. When forming the separation groove,the layer between the n-type contact layer and the substrate may beexposed, or the separation groove may be formed so as to expose thesubstrate. Moreover, in case the separation groove is formed by exposingthe substrate, the substrate may be etched midway thereby to expose thesubstrate.

[0310] The regions for defining the devices may not be necessarilyformed for each device, and a region to constitute two devicescollectively may be formed as described in the tenth embodiment, or aregion to constitute three devices collectively may be formed (forexample, portions III and IV shown in FIGS. 17A, 17B are formedcollectively).

[0311] Similarly in the direction perpendicular to the light guidingdirection, a plurality of regions may be formed continuously withoutforming separation grooves between the devices.

[0312] Cracking and chipping in the active layer due to the impact ofdivision can be avoided by forming the groove by etching deeper than theactive layer and dividing along the groove (for example, portion A-Ashown in FIG. 17A, FIG. 17B).

[0313] In the eleventh embodiment, the region for each device isseparated to make the individual devices. Then similarly to the tenthembodiment, the stripe ridges for constituting the waveguide regions areformed and then the first waveguide region C₁ and the second waveguideregion C₂ are formed in each region corresponding to each device. Thefirst waveguide region C₁ is formed with stripe length of 10 μm.

[0314] Then similarly to the tenth embodiment, a p-type electrode ofstripe shape having a width smaller than the width of the p-type contactlayer is formed on the surface of the p-type contact layer only in thesecond waveguide region C₂. At this time, the p-type electrode of stripeshape is formed in such a length that does not reach the end face of thesecond ridge which constitutes the second waveguide region C₂ so as tokeep away a little therefrom.

[0315] Then an n-type electrode is formed on the back side of thesubstrate (the surface which opposes the substrate surface whereondevice structure is formed), Then similarly to the tenth embodiment, theinsulation film (reflector film) 164 made of dielectric multi-layeredfilm is formed over substantially the entire surface on the side of thesubstrate where the device structure is formed and, with a part of thep-type electrode being exposed, a pad electrode is formed so as toelectrically connect to the exposed p-type electrode.

[0316] Last, laser devices in the form of chips are obtained by cleavingat the D-D cutting position located substantially at the center of thefirst waveguide region C₁ as the cutting direction perpendicular to theresonator and along the M plane of the substrate at the A-A cuttingposition between the devices thereby to separate into bars and thencleaving between the devices along A plane perpendicular to the cleavageplane.

[0317] The laser device obtained as described above has the cleavagesurface at the end of the first waveguide region C₁ and the etched endface whereon the reflector film is provided at the end of the secondwaveguide region C₂ as the resonance end faces, and is capable of laseroscillation. The laser device obtained as described above has excellentlaser characteristics similar to those of the tenth embodiment.

[0318] [Embodiment 12]

[0319] The laser device of the twelfth embodiment is made by forming theresonator end faces simultaneously as etching down to the n-type contactlayer, and dividing the substrate between the resonator end faces alongthe AA cut surface in I and II of FIG. 17A after etching down to thesubstrate, in the eleventh embodiment. At this time, the dimension ofthe portion protruding from the resonator end face is set to 3 μm. Thelaser device obtained as described above has excellent lasercharacteristics similar to the device characteristics and opticalcharacteristics of the eleventh embodiment.

[0320] [Comparative Embodiment 1]

[0321] As a first comparative embodiment, a laser device having thesecond waveguide region C₂ formed over the entire length thereof withoutforming the first waveguide region C₁ in the first embodiment isfabricated.

[0322] In the first comparative embodiment, different layers whichconstitute the device structure are stacked one on another similarly tothe first embodiment. Then as shown in FIG. 5B, the second stripe ridgeis formed to extend from one end face of the device to the other endface, by using the first protective film 161 as the mask.

[0323] Then a protective film made of ZrO₂ is formed on the side face ofthe first ridge formed over the entire length thereof and on thesurfaces on both sides thereof which are exposed by etching. The waferis then dipped in hydrofluoric acid thereby to remove the firstprotective film 161 by liftoff. Then similarly to the first embodiment,the resonance end face and the electrodes are formed thereby to obtainthe laser device of the first comparative embodiment which has only thesecond ridge for constituting the second waveguide region C₂.

[0324] In the laser device of the first comparative embodimentfabricated as described above, it is difficult to effectively suppressthe unnecessary transverse mode, thus resulting in lower stability ofthe transverse mode and frequent occurrence of kink in thecurrent-optical output characteristic.

[0325] Particularly in a high output range of large optical outputpower, for example, output power of 30 mW which is required to writedata in an optical disk system, shift of the transverse mode is likelyto occur. Also because the device characteristics are sensitive to thedimensional accuracy of the second ridge of stripe shape, significantvariations occur among the devices thus making it difficult to improvethe yield of production as shown in FIG. 10. The aspect ratio of thelaser beam spot mostly fall within a range from 2.5 to 3.0, which meanssignificantly low yield of production provided that the criteria ofacceptance for aspect ratio is 2.0 or lower.

[0326] Now the result of investigation conducted to verify the effectsof the constitution of the laser device according to the presentinvention (service life of laser device, drive current andcontrollability of transverse mode) will be described below.

[0327] In the investigation, device constitution (laminated structure ofsemiconductor) similar to the first embodiment was used to fabricate thelaser devices of different ridge height while changing the depth ofetching, and the service life of laser device, drive current andcontrollability of transverse mode were evaluated on the laser devices.

[0328]FIG. 12 shows the service life of the laser device (tested withoptical output power of 30 mW) for different depths of etching.

[0329] As shown in FIG. 12, when etching is carried out to a depth nearthe boundary of the p-type cladding layer and the p-type optical guidelayer, device life becomes longest but the life becomes shorter when theetching depth is smaller. Also when etching near to the boundary of thep-type cladding layer and the p-type optical guide layer, the laserdevice decreases abruptly, indicating that there occurs an significantlyadverse influence on the device life when the stripe waveguide region isformed by etching to a depth that reaches the active layer. When thedevice life is taken into consideration, therefore, it is better to etchto a depth which does not reach the p-type electron confinement layer.Also it can be understood that, when the ridge is formed by etching to adepth in a range of 0.1 μm above and below the boundary between thep-type cladding layer and the p-type optical guide layer, very longservice life is obtained. When the confinement of light in the directionof thickness is taken into consideration, it is preferable to etch tosuch a depth which does not reach the p-type guide layer. With thisrespect, it is more preferable to carry out etching to a depth of 0.1 μmabove the interface of the p-type cladding layer and the p-type opticalguide layer.

[0330]FIG. 10 is a graph showing the acceptance ratio for differentdepths of etching. From FIG. 10, it can be seen that a high acceptanceratio can be achieved by etching to a depth deeper than a point 0.1 μmabove the interface of the p-type cladding layer and the p-type opticalguide layer. The acceptance ratio shown in FIG. 10 indicates whatproportion of devices which have proved capability to oscillate canoscillate in the fundamental single transverse mode at 5 mW, while thestripe width of the waveguide region at this time was 1.8 μm.

[0331] When etched to such a depth as 0.1 μm or more of the p-typecladding layer remains on both sides of the ridge, kinks occur abruptlythus leading to a significant decrease in the acceptance ratio.

[0332]FIG. 11 shows the drive voltage (with optical output of 30 mW) asa function of the depth of etching, with the width of the waveguideregion being set to 1.8 μm for the investigation. As will be clear fromFIG. 11, the drive current remains constant at 50 mA regardless of thedepth of etching, when etching is carried out deeper than the mid pointof the p-type optical guide layer (mid point in the direction ofthickness) on the active layer side. When the depth of etching isdecreased from the mid point of the p-type optical guide layer, thecurrent gradually increases up to 0.1 μm above the boundary of thep-type cladding layer and the p-type optical guide layer, while thecurrent sharply increases when the depth of etching is shallower than0.1 μm above the boundary of the p-type cladding layer and the p-typeoptical guide layer (such a depth of etching that a thickness of 0.1 μmor more of the p-type cladding layer remains on both sides of theridge). When etched to such a depth as thickness of 0.25 μm or more ofthe p-type cladding layer remains, it becomes impossible to achieve anoptical output of 30 mW.

[0333] [Comparative Embodiment 2]

[0334] As a second comparative embodiment, a laser device having thefirst waveguide region formed over the entire length thereof withoutforming the second waveguide region in the first embodiment isfabricated.

[0335] In the second comparative embodiment, different layers whichconstitute the device structure are stacked one on another similarly tothe first embodiment. Then as shown in FIG. 5A, the ridge of stripeshape which constitutes the first waveguide region C₁ is formed byforming the first protective film 161 of stripe shape and etching theregions on both sides of the first protective film to such a depth thatreaches the lower cladding layer 5. Then a protective film made of ZrO₂is formed on the top surface and the side face of the ridge and on thesurfaces on both sides thereof which are exposed by etching. The waferis then dipped in hydrofluoric acid thereby to remove the firstprotective film 161 by lift-off. Then similarly to the first embodiment,the resonance end face and the electrodes are formed thereby to obtainthe laser device which has only the first waveguide region C₁ with thesectional structure as shown in FIG. 9. In the second comparativeembodiment, the stripe ridge is formed by etching to such a depth asthickness of 0.2 μm of the p-type cladding layer remains on both sidesof the ridge similarly to the first waveguide region C₁ of the firstcomparative embodiment.

[0336] The laser device thus obtained has shorter service life than thatof the first embodiment since the stripe is formed by etching deeperthan the active layer, and does not make a practically useful laserdevice with the service life as short as shown in FIG. 12.

[0337] The laser device of the present invention has the first waveguideregion C₁ and the second waveguide region C₂ as the waveguide in theresonator direction, and therefore provides excellent device reliabilityand controllability of transverse mode. The present invention alsoprovides laser devices of various device characteristics with simpledesign modifications.

[0338] While it has been difficult to achieve excellent devicecharacteristics of conflicting items such as practical level of devicereliability and stable oscillation in the transverse mode at the sametime, the laser device of the present invention combines excellentproductivity, reliability and device characteristics. Moreover, it ismade possible to obtain laser beams of various spot shapes and variousaspect ratios by providing the first waveguide region C₁ partially onthe light emitting side of the resonance end face. Thus the presentinvention is capable of achieving various beam characteristics and has agreat effect of expanding the range of applications of laser device.

[0339] In the nitride semiconductor laser device of the prior art,satisfactory yield of production and productivity can be achieved onlywith striped laser device because of the difficulty in the regrowth ofcrystal and in the implantation of ion such as proton. When the activelayer having nitride semiconductor which includes In, significant damageis caused and the service life of the device decreases significantly,and therefore only the effective refractive index type laser devicecould be selected. In contrast, the laser device of the presentinvention has the first waveguide region C₁ and the second waveguideregion C₂ and therefore achieves controllability of transverse mode andexcellent beam characteristics while ensuring reliability of the device.Also the device structure allows manufacturing with high yield ofproduction even in volume production and makes it possible to apply anddrastically proliferate the nitride semiconductor laser device.Moreover, when used as the light source for an optical disk system ofhigh recording density, such an excellent laser device can be providedthat is capable of operation over 1000 hours with 30 mW of output powerand aspect ratio in a range from 1.0 to 1.5 without shift of transversemode in the ranges of output power for both reading data (5 mW) andwriting data (30 mW).

1. A semiconductor laser device comprising a laminate structureconsisting of a semiconductor layer of first conductivity type, anactive layer and a semiconductor layer of second conductivity type,which is different from the first conductivity type, that are stacked inorder, said laminate structure having a waveguide region to guide alight in a direction perpendicular to the direction of width, saidwaveguide region being formed by restricting the light from spreading inthe direction of width in the active layer and in the proximity thereof,wherein the waveguide region has a first waveguide region and a secondwaveguide region, the first waveguide region being a region where lightis confined within the limited active layer by means of a difference inthe refractive index between the active layer and the regions on bothsides of the active layer by limiting the width of the active layer, andthe second waveguide region being a region where the light is confinedtherein by providing effective difference in refractive index in theactive layer.
 2. The semiconductor laser device according to claim 1;wherein said first waveguide region has the active layer of which widthis restricted by forming a first ridge so as to include the activelayer, wherein said second waveguide region constituted by including aregion having effectively higher refractive index caused by forming asecond ridge in the layer of the second conductivity type.
 3. Thesemiconductor laser device according to claim 2; wherein said firstridge is formed by etching both sides of the first ridge until the layerof the first conductivity type is exposed and said second ridge isformed by etching both sides of the second ridge so that a part of thelayer of the second conductivity type remains on the active layer. 4.The semiconductor laser device according to claim 3; wherein a thicknessof the layer of the second conductivity type located on the active layeron both sides of the second ridge is 0.1 μm or less.
 5. Thesemiconductor laser device as in one of claims 2-4; wherein said secondridge is longer than said first ridge.
 6. The semiconductor laser deviceas in one of claims 1-5; wherein said first waveguide region includesone resonance end face of the laser resonator.
 7. The semiconductorlaser device according to claim 6; wherein said one resonance end faceis a light emitting face.
 8. The semiconductor laser device as in one ofclaims 1-7; wherein a length of said first waveguide region is 1 μm ormore.
 9. The semiconductor laser device as in one of claims 1-8; whereinsaid semiconductor layer of the first conductivity type, said activelayer and said semiconductor layer of the second conductivity type areformed from nitride semiconductor respectively.
 10. The semiconductorlaser device as in one of claims 1-9; wherein said active layer isconstituted from a nitride semiconductor layer which includes In. 11.The semiconductor laser device as in one of claims 1-10; furthercomprising insulation films on both sides of said first ridge and onboth sides of said second ridge, said insulation films being made of amaterial selected from the group consisting of oxides of Ti, V, Zr, Nb,Hf and Ta and compounds SiN, BN, SiC and AlN.
 12. A semiconductor laserdevice comprising; a laminate structure being consisted of a layer ofthe first conductivity type, an active layer and a layer of the secondconductivity type that is different from the first conductivity typebeing stacked in order, said laminate structure being provided with astripe waveguide region, wherein said stripe waveguide region has atleast a first waveguide region C₁ in which a stripe-shaped waveguidebased on absolute refractive index and a second waveguide region C₂ inwhich a stripe-shaped waveguide based on effective refractive index,which are arranged in the direction of the resonator.
 13. Thesemiconductor laser device according to claim 12; wherein the absoluterefractive index of said first waveguide region C₁ is achieved by meansof the stripe ridge which is provided so as to include the layer of thefirst conductivity type, the active layer and the layer of the secondconductivity type, and the effective refractive index of said secondwaveguide region C₂ is achieved by means of the stripe ridge which isprovided in the layer of second conductivity type.
 14. A semiconductorlaser device comprising a laminate structure including a layer of thefirst conductivity type, an active layer and a layer of the secondconductivity type that is different from the first conductivity typebeing stacked in order, said laminate structure being provided with awaveguide region of stripe configuration, wherein said stripe waveguideregion has at least a second waveguide region where a portion of thelayer of the second conductivity type is removed and a stripe ridge isprovided in the layer of the second conductivity type, and a firstwaveguide region C₁ where portions of the layer of second conductivitytype, the active layer and the layer of second conductivity type areremoved and a stripe ridge is provided in the layer of the firstconductivity type, which are arranged in the direction of resonator. 15.The semiconductor laser device as in one of claims 12-14; wherein saidfirst waveguide region and said second waveguide region are constitutedby removing a part of the laminate structure and forming a ridgewaveguide comprising a stripe ridge.
 16. The semiconductor laser deviceas in one of claims 12-15; wherein said a length of the second waveguideregion is longer than said first waveguide region.
 17. The semiconductorlaser device as in one of claims 12-16; wherein at least one of theresonance end faces of the semiconductor laser device is formed at theend of the first waveguide region.
 18. The semiconductor laser deviceaccording to claim 17; wherein a resonance end face formed on the end ofthe first waveguide region C₁ is a light emitting face.
 19. Thesemiconductor laser device as in one of claims 17, 18; wherein a lengthof the first waveguide region which has the resonance end face on theend face thereof is 1 μm or longer.
 20. The semiconductor laser deviceas in one of claims 12-19; wherein said semiconductor layer of the firstconductivity type, said active layer and said semiconductor layer of thesecond conductivity type are formed from nitride semiconductorrespectively.
 21. The semiconductor laser device according to claim 20;wherein said active layer is constituted from a nitride semiconductorlaser which includes In.
 22. The semiconductor laser device as in one ofclaims 20, 21; wherein said semiconductor layer of the firstconductivity type include n-type nitride semiconductor and saidsemiconductor layer of the second conductivity type include p-typenitride semiconductor.
 23. The semiconductor laser device according toclaim 22; wherein said second waveguide region has a p-type claddinglayer which includes p-type nitride semiconductor and the stripe ridgeof the second waveguide region is formed while keeping the thickness ofthe p-type cladding layer is less than 0.1 μm.
 24. The semiconductorlaser device as in one of claims 20-23; wherein a side faces of thestripe ridge of the first waveguide region and a side faces of thestripe ridge of the second waveguide region are exposed, and aninsulation film is provided on the side face of the stripe ridge, saidinsulation film being made of a material selected from the groupconsisting of oxides of at least one element selected from Ti, V, Zr,Nb, Hf and Ta and at least one kind of compounds SiN, BN, SiC and AlN.25. The semiconductor laser device as in one of claims 20-24; wherein awidth of said stripe ridge is in a range from 1 μm to 3 μm.
 26. A methodfor manufacturing the semiconductor laser device comprising; alaminating process in which the layer of the first conductivity type,the active layer and the layer of the second conductivity type arestacked in order by using nitride semiconductor to form a laminatestructure, a process of forming a first protective film of stripeconfiguration after forming the laminate structure, a first etchingprocess in which the laminate structure is etched in a portion thereofwhere the first protective film is not formed thereby to form the striperidge in the layer of the second conductivity type, a second etchingprocess in which a third protective film is formed via the firstprotective film on a portion of the surface which has been exposed inthe first etching process and the laminate is etched in a portionthereof where the third protective film is not formed thereby to formthe stripe ridge in the layer of first conductivity type, a process inwhich a second protective film having insulating property made of amaterial different from the first protective film is formed on the sideface of the stripe ridge and on the nitride semiconductor surfaceexposed by etching, and a process of removing the first protective filmafter the second protective film has been formed.